Strain Gages

CIVIL ENGINEERINGMANUALSgb.30.09.02 Instrumentation, NSEL C&EE U ffiUC StrainGauges:Theory,Instrumentationand Installation SecondEdition Preparedby: GrzegoruBanasand Can Simsir by:NewmarkStructuralEngineeringLaboratory Sponsored Departmentof Civil & Environ.Engineering Collegeof Engineering Universityof Illinois at Urbana-Champaign Urbana.Illinois 61801-2397 September,2002 NEWMARKSTRUCTURAL ENGINEERINGLABORATORY z What is a sh'ain.gauec? It is a kansducerthat allows the measurementof deformation (strain) in any material. Mechanical,optical, and electricalprinciples havebeenemployedin the processof designingstrain gauges. Types of electricalstrain gaugesinclude the resistance, inductance,and the piezoelectricstraingauges.Due to their versatility,small size capacitance, and weigfut,as well as high sensitivityto the measuredstatic and dynamicstrain, electrical resistance straingaugeshavebecomethe mostpopularin researchandindustrialapplications.In straingauges(straingauges)will be discussed. this manual,only the electricalresistance metalfoil Figure2a showsan exampleof a commonlyusedstraingauge.A photo-etched alloy is the oldestandthe patternis mountedon a plasticbackingmaterial(carrier). Constantan giass-fiber reinforcedepoxy-phenolicare commonly most widely usedmetal. Polyimideand used as backing materials. Each strain gaugehas a specific designationthat describesits (Figure2b). characteristics Florvdoes the strain gaugelvork? When the strain gaugeis subjectedto a potential differenceff) (Figure 3), current(i) is generated.The magnitudeof cunent (i) dependsupon the (R) of the straingauge: resistance D (R) of the grid wire is a functionof its resistivity(p), length(l), and cross-sectional Resistance (A): area R= o: I A Assuminga constantpotentialdifference(V), the magnitudeof current(i) will vary with the grid wire's length (1) and its cross-sectionalarea (A). Therefore, if a shain gaugeis bonded to a materialexperiencingsurfacedeformation,current(i) will alter accordingto that deformation area(A) of the grid wire. When strain due to changesin the length (l) and cross-sectional (A) (l) decreases, and for most materialsthe resistivity area increases, the wire length increases, (p) increases,These.changesresult in an increasein the resistance(R) of the wire. This relationship between wire resistanceand strain is linear at constant temperature,and it is by the gaugefactor(K). expressed What is the eaugefactor (K)? A strain gaugecorrelatestwo physicai quantities: change relationshipbetweenthesetwo variablesis in resistance andchangein strain. The dimensionless calledthe gaugefactor (K) of the sffain gaugeand it is expressedmathematicallyas: % K - ^/t where (R) and (1) represent,respectively,the initial resistanceand initial length of the strain gaugegrrd wire, while (AR) and (A1)representthe small changesin resistanceand length which occut as the gaugeis strainedalong with the surfaceit is bondedto. Equation 5 assumesthat Poisson'sratiov=0. 2 Straingauge:a) geometry.Open-facedgeneral purposegaugewith tough flexible castpolyimide backine Self-TemperatureCompensation S-T-C numberis the approximate thermalexpansioncoefficient in ppn/'F of the structural on which the eauseis to be used Fig.b) designation.Grid width a) 50 bo (.) (!) o oo !9 (!t acking Foil pattern Carrier matrix (backing) E . . The rnagnitudeof cunent (i) could be calculatedusingOHM'slaw.) is a function of the grid wire's length (l). 4 Wheatstone-bridge circuit (a) andits mechanicalanalog@). E e=j R=* I tl p -J- J=! A I R=pa Where: (E) is the electricfield density. b) &=& R4& Fig. .4 t. 3 Straingaugewhich experiencesa potentialdifference(V). (J) is the cunent density Fig. andresistivity (p). Resistancefi. its cross-sectionalarea(A). 0r0.000 lrI = 0.0080: 8 mo AR= Ri(? = 120c2. kr Figure4a. the strain (e) could be calculatedby rewriting Equation5: ^R/R N IK In other words. They are not capableof measuringresistancewith suffrcient are not recommended circuit is precisionto detect such small differences.) and gaugefactor K = 2'0 is usedfor Example: Straingaugeof resistance of stess of S = 1. then the voltage across (V4 . the unit skain (e) equalsto the unit changein resistance(AR. then: galvanometer Va-^=Va-cor \& =k& and V"-o=Vc-o or iR4 =i24 6 Dividing Equation7 by Equation8. and (R4) is a resistancewhosevalue is known precisely. s 5=r.000psi.6) is alsoequalto zero(V.R) divided by the gaugefactor (K). Sincemodr. tlen the corresponding elasticity(E) for steelis approximately 1"000 -0.c:0). That is why the Wheatstone-bridge commonlyused.001O shallbeused. the conventionalohmmeters to use.) circuit is used as a basic What is th.ebasic instnunentation?A Wheatstone-bridge of sfain is an equivalent Ttrc magnitude Figure 4a. of (AVl) ftom Equation 5 and is proportional to (ARtR).rlus of specimenexperiencing strainmeasurement .: -::-:E 30. an instrumentwith the resolutionof at least0. When resistancevaluesin this circuit are such that no current flows through the galvanometer(i6 : 0). assumethat (R1)is an unknownresistance. R = 120 f. A changein resistance(AR) is the only unknown in Equation 6. (Rz) and (R:) are "tatio atms". currents(ir) and(iz) couldbe eliminated: fromwhich +=+ n =*n R4R34 s A mechanicalanalogof the wheatstonebridge is shown in Figure 4b. Since botl gauge factor (K) and resistance@) areknown. Since the magnitudeof (AR) is relatively very small (it is in the rangeof mO).000.000033in/in. Sincei6= 0. The unknown weight in this figure representsthe unknow:r resistance(R1) and the small known weight the .t . unit strainis: 3O 166psi. see inskumentationfor strain measurement.000033 I It is apparentfiom these calculationsthat in order to determineAR. This processof adjusting is equivalentto charigingthe weiCht(It4) rurtil no motion of the lever is achieved.and the other two gaugeshave equal strainsthat are oppositein sign to the frst two strains. From elementarystatics it is obvious that when the lever is in a state of balance. The strainsfrom the two gaugesare equalbut opposite in sign and thushelp increasethe sensitivityof the circuitry. In a Full bridge.andin Ref.This type of bridgecanbe usedto goodadvantage the gaugeson two oppositearmsof the circuit haveequalshains. specimen. hstead of re-balancingthe bridge after loading the specimen.Anotherb?e ofpracticalWheatstone the Half bridge with only two active gaugeson any two adjacentarms of the circuit.attachedto the surfaceof the loaded (AR) will foliow. If the skain gauge(R1).then the sensitivity (the output of the bridgecircuit)is increased by morethana factoroftwo. Similarly the respectivemomentarms of theseweights from the firlcrum are the equivalent of @2) and (R3). 19. Just as the lever systemis termed "balanced"when thereis no rnotionof the endsof the lever. Ra = Rz . In practice. fu. thus determining the exact resistance of the gaugethatconesponds to zeroload(ic = 0). If activegauges.thechangeof its resistance circuit hasbeenprimarilyusedto estimate(AR). Bridgecanalsobe balancedusingan adjustable resistor(R4). The Wheatstone bridgediscussed aboveis caiieda Quarter bridge becauseonly oneof the four armsof the Wheatstone bridgehasan activegauge(R1).experiences anystrainchange. 2. The processof adjusting the ratio (Rz/Rt) is equivalent to moving the ftilcrum of the lever systemuntil the weightsin Figure4bjust balanceeachother. Quarterbridge is usedwhen bridgeis singiestrainsin a stressfield areto be measured. the galvanometer readingis proportionalto the resistancechangeor strain.the resistor can be determinedvery accuratelywith the Wheatstone-bridge (Rt) is an active straingauge. A typical applicationof Half bridge is on a other fixed resistances cantileverbeamto determinebendingshainsby instrumentingthe tensionand compressionsides eachwith one active gauge(Figure 5a). 3.then R1 . is calibratedin strain In practice. With ths resistor @4) whose value is known to a high no curent through the of (R1) degreeofprecisionandwith meansof measurilgtheratio R2/R3precisely. ali fow armshave in a ioad cell (Figure5b). Bridge can be balancedby adjustirg the ratio (RzlR:).optionnumber3 is usedin whichtheoutputfrom galvanometer units.6 resistor (R4). For small changesin the resistance(Rr).the galvanometer indicationitself might be taken as a measureof strain. This could be The Wheatstone-bridge doneusing threedifferent approaches: 1. More detailed information on practical Wheatstone-bridgecircuits and their applicationsis availablein Chapter7 of Ref. 16.so is the Wheatstone bridge"balanced"whenthereis galvanometer. and two to completethe bridge. .tle resistance circuit. 5b Application of Full Bridge. 5a Application of Half Bridge. .I CantileverBeam: R1on tensionside R2on compr€ssionside l--l -Ann- Active gauge Fixed resistance Fig. CylindricalLoadCell: Comnressive Rr && in compression Rz&& in tension l----l Active gauge Fig. c) powersupply.b) singlechannelsignalcondifioner/amplifier. 6 Four channel. d) input box.Y 11 POWER n OFF 2 AO. I oo Fig.a) ChannelI Channel2 Channel3 Channel4 Powersupply Outputcables J c) oc co 3 oA BO OD oO Oe GO Oe sO Oa HO Or rO Os HO OF FO OIr GO OE EO OG BO OD DO OB OC "o4 Ao CIIANNEL .2100 straingaugeconditionerand amplifier system(yellow box): a) picture of-the21fi) system. I DC---J aa- | E)ffERNAI-METER -OO+U POWERSIJPI{.ffi. breakout . 10 r-o L-> L--__>E E Active strain gauge A C F A H (120fl) |'t (350O) F Quaterbridge: internaldummy.r A D c F Half bridge: alternate. . Activestrain (compression or compensation) R=Rl+R2 Halfbridge: prefened. F Full bridge: ffansducer. ]. * Input A ]. Fig. E B Active strain gauge Dummy snaingauge or resistor Activestraingauge (tension) A Activestrain (compression or compensation) Quaterbridge: extemaldummy.7 Inputbreakoutbox'scircuits. r--o L-> r_->E Full bridge: straingauges. -.Ref. with a 120 proves inadequatefor the gaugesor reducedto under +700 pe' If the balancerange replacedor shunted with an transducersin use.ri* U. tut ".and(R"uil is the calibrationresistance and"BALANCE" (points4 and 5) on each 8. ro.. sucha way that iO viC o"tp* to""'pond' to is 30'000 pe (3%' 3 ' 10-2)' In example: The maximumexpectedit'uin to be measured berngused.u. *a cost * analog our dataloggilg systems'which are capableof storhg This requirementalso comesfrom the limitation of sisrals at the *10 VDC level onlY' .*c" will be reduced for lorver bridge resistance other than 350 Q. G maximurnstrainexpected-'For knob i.[*r"i. B A I .A N C E ' ' r e s i s t obridge r c a ninputs correctforan or firll bridge' With quarter' half O in 350 pe +2./. .y.000 ue = ?o ooo rr_c l0 U. strain range. voltagemustbe: simulatetension(toggleswitchiln"A" position). T h e .*t th" giin usingboth ". gaugepl$em' sef-tempe'atorecompensation of measurement.1l l i g h t s ( + a n d ) s h o u l d b e e x t i n g r r i s l r e d . 6..the output ll = " out ljV o1.' .000 *tA*"! approximately and . Usingthe toggleswirchA-OFF-B(Figure6b) for (positionA) or compression(positionB)..=iL(&rt4)*ro' in (O)' (K') is the effective where(Rr) is the preciseeffectiveresistanceof arm shunted in (Q)' gaugefactor of straingauge. ri. srueyou know the resistorcolor channelsused' When ttittg * additionalresistoi'make codeavailablein Ref. Assuming l. . Connectthevoltmeterto an "output channel1' a strainof 1'000 (Figure6a)... "AMp zERo on an extendedtest' occasionallY INSTALLATION the mostimportantstepin any stratn Srain gaugeselection'Selectionof straingaugesis (teipeiature range. the tulanc" tesistor should be either Repeatthis procedurefor all additionalone.i-ututJa eitheiln tension ud. rhe .) of strain measurement.J. It is advisableto checkboth "AMP ZEROBAL' BAL" (point 4) shouldbe checked charrneljust beforedata .The2100systemhasashrrntcalibrationbuiltintotheconditioner/amplifierwhichsimulates cable"conespondingto channel1 a strail of 1. backing materials (carriers). The operating . 20.. u""u. etc..ujoilJ.when shuntbridgecalibrationis usedto spireof the resisrance "l. gaugesare affected uy man! paramete$ (strail-sensitive ttu-b"t' grid resistance'etc') which gaugelength.JJJ. .l* alioy.GAN' screwand the maximumstrainro b..000pe..Ifarrextemalshuntcalibrationisselected.rir. .themagnitudeofsimulatedstraincanbe calculated: 1I tE*.il"*n. o full bridge' the balancerangeis increasedfor higher onrrl roi t*uitprt."1'l"Lirity. l provides a partial eventuallydeterm*. The ratt"i option is usedin the applications.. Solderingprocedureis essentialto the strain gauge wiris.It is recommendedto follow this procedure.4 presents adhesives recommended alsoa procedurewhich couldbe usedfor most straingaugeapplicationsin our laboratory.who will then make of thetest.Follow the proceduredescribedin Ref.The resistance Temoerature is conholledby the coeffrcientof thermalexpansionof the variation This changein resistance alioy from which the strain gaugeis fabricated. essentialreductionofthe initial imbalanceofthe bridge. it is recommendedto use the list of straingaugemanufacturers selectionproiedure presentedin Ref. 4 provides a list of rutfu.. . 1. Strain gauee installation.affectthe qualityof the p".fo* t**ting iolderedjoints. This temperaturecompensationis not quite perfect. 16). 3. but over a rangeof about-20'c to +120'c the e or is small enoughto be corrected temperature from a graph of strain gaugeerror versustempefature. a selectionbasedon the userdescriptions of a strain gaugechangeswith temperature compensation.t2 (copiedfrom Ref. The procedurepresentedin Ref.the specimenandthe gaugeenvironment. 1) can be completedand irt"tnJto either authorsof this manualor the Micro-MeasurementsGroup. of the straingauge.r leadwire 4O A" sr*utt jumper wires to the strain gauge. i. **ily for differentstraingaugeseries(copiedfrom Ref. If bondableterminals are usedbetweenthe mai.The procedurepresentedin Ref' 6 is recommendedfor applicationof bondableterminals' Threewires versustwo wires for quarterbridse circuits. soideringiron. Also. . in the caseof any temperanrrevariation. straingaugeswhich must be usedon materials Applicationof temperature-compensated for which they havebeencompensated. effects' on straingaugetemperature Ref. Strain gaugesolderingtechniques.suppliedby the manufacturersof the gauges. solderingallon flux. forces transmitted along the main leadwire systemcanbe preventedfrom damagingthe straingauge. Ifthe useris unsureof whatgaugeto choose. It is recommendedto use (three) 3 wires in the quarterbridge circuits for the followtng reasons: . 2 providesa detaileddiscussion Surfacepreparation. of a 'dummy'gaugewhich must be placedclose enougbto the active Al application -to gurrg" enswe that it will remain under all conditions at the sametemperatureas the activegauge. Ref. Ref. etc. Also. As a the thermalexpansionof the gaugedmaterialchangesthe resistance to minimizeerrors available are occur. Two methods errorsin strail measurement consequence.a'strain gage applicationrequirements'form (includedat the end of Ref. dueto temperaturevariation: . The procedureof installing a strain gauge to_the material associatedwith a type of adhesiveused.The temperaturecompensationis controlledby a choiceof suitableconstituentsof the strain gaugealloy and suitableheatkeatmentduring its manufacture. 16). 5 is recommendedfor usage' Use of bondableterminals. Measurements Group. TECH NOTE. StrainGageSelection. 3 Surface Preparation for Stmin Gage Bonding. TN-505-3(included). (copiedfrom Ref.saltwatff. Spot-weldingofthe gaugeto the specimeneliminatesthe needfor all bondingmaterials. . The Mcoat A protectivecoatingkit is recommendedfor usage. Moistureis the mostcommoncauseof field installationfailures.rimentswith concrete structuresis quite common at NSEL.The M-coat F is recommendedfor strain gaugeapplicationson reinforcementbars in concrete.Ref. 1 Group. Weldablestraingauges.TECHNOTE. electricalnoise. Ref. Ref. I describes themostcommonlyusedM-coatprotectivsesnlingkits.13 . and strain gauge application for concreterequires a different and more chalienging procedure.dependingon which causeis predominant. The procedureof using3 wires presentedin Ref. Strain gauge for concrete. 16). extremetemperatures.wiring technique.Ref. Gaugeselection. steam.etc. 7 is recommendedfor practice.anddesensitization pathscan also form.and a portablestraingaugeweldingunit.TN-504-1(included). bettersensitivity.requires minimal surface preparation and reducesinstallation time.129-7(included). M-coat F protectsthe strain gaugefrom moistue aswell astheimpactof aggregates in concrete.Procedures. Ref.handling excessleadwiresand cablescan play an important role in controlling this noise.Criteria. . Measurements Recommendations. The installation of weldablestrain gaugesrequirescapacitivedischargespot-weldingequipment. Instnrction BulletinB. Measurements Group. 4 Strain Gage krstallations with M-Bond 200 Adhesive. 11 describesa few of the weldablestraingauges.Theseruggedandstablegaugesarebettersuitedfor applications in severeenvironments. Grid corrosionandintragridconductive of themeasurement.Inc. MeasurementsGroup. RIFERENCES Ref. 10 providesinformationon detectingandreducingelectricalnoisein measurements. causingnegativeor positivedrift in output. Also providedis a selection chartfor weldablestraingaugescourtesyof Ailtech.such as shoclg vibration. Noise control in measurements. Protectivecoatine. Electrical noise in strain measurementsis due to electrostaticand electromagneticfields in the straingaugeenvironment. 9 describesthis procedwe. 2 Strain Gage Thermal Output and Gage Factor Variation with Temperature. fundamentalreductionof errorthat resultsfrom temperaturechangesin the leadwire system. Expe.as well asprovidesinstallationand instrumentation tips for'embedmentstraingauge'speciallydesignedfor usein concretestructures. Ref. Ref. InstructionBulletinB-127-13(includeO. Its presenceusually results in 1ow eiectricalresistanceto ground causingcirculating currents. Ref. BulletinSFC-800-3(partlyincluded). 9 Strain Gage Installations for ConcreteStnrcfiues. Instnrction Manual (included). 17 http://www. G. TNRef. H. R. 501-2(included). C. 15 Dally. Shain Gages.html Ref. Measurements (included). and Riley. Principlesof EngineeringInstrumentation. W. group Ref.20 http://kelim.html . Ref.cee.edu/me82/LeamindStrain/strain.1965. 14 Perry.t4 Ref. Ref.jct. 11 An Introductionto. and Lissner. TECH TIP.C. Ref.Installation Ref. J.publishedby McGraw-Hill Book Cornpany. TECH TIP' TT-609 (included). 16 Ha:ris. Ref.MeasurementsGroup. Measurements Group.. 5 Shain Gage Soldering Techniques. 19 http://www.MeasurementsGroup. EGP-Series.MeasurementsGroup.iVelectronics/webprogs/resistor/resistor. C. Ref. Bulletin321 (included).G.ac. TT-612 The Three-WireQuarter-BridgeCircuit.D. StructuralModeling and ExperimentaiTechniques. W.134-4(included).H. TT-611 (included)./brands/measurements Ref. publishedby HalstedPress.Measurements Group. i3 Ramsay. 6 The ProperUse of BondableTemrinalsin Strain GageApplications. Micro-Measurements Accessories. Strain GageConditionerand Amplifier System.1955.8 M-Coat A protectivecoatingkit.publishedby McGrawHill Book Company. The StrainGagePrirner.com. F. 12 2100 SYSTEM. EmbedmentStrain Gage.osu. TECH TIP. and Sabnis. MeasurementsGroup. 1996. TT-603(included).1999.me. _ Ref.vishay. SecondEdition.TECH TIP.InstructionBulletinB. 18 http://www.edu/classes/cee398kuc Ref. M-Coat F ApplicationIastructions. Ref.7 Group.. M.SpecialSensors. 10 Noise Contol in Strain GageMeasurements. Ref. ExperimentalStressAnalysis.TECH NOTE.uiuc.Measurements Group. Reference1 . 83 Ellington.sBain. rcB Piezoronics.dara acquisitionsystems Servo-controlledloading Dxtr arquisirionsyst{Irs St.Box429 Wallorv Crov€.com Box 24012 Minnespolis. CA 91786 rel:(714)946-t000 fa( (7 14)946-626'7 2048Bunn€llRd.2 PartialList of Manutacturersof DifferentTypesot Instruments Manufacturer A.V McaluementsGrcup. JPTechnologies. Box 1089 T!oy.CT 06029 rcl:(860)872-8371 tcl: (800)828-39€'4 fax:(860)872421| Essbn Rd.TX 78730-5039 tel:(512)?94-0100 far: (512)794-841I An OMEGATcchnologics Co. TRANS-TEK Tini0s-OlsenTesdns MachineCo.L.. PO. Eaton Corp Corp. Canton. PO. Address l4l I MiliraryRd8uffalo.and instrumcnution. Inc. Inc. PO. Ausrio.PA 19090-0429 rcl:(215)675-7100 fir: (2I 5) 44| -0899 Types of Accessories SensoN. Box 27771 Raleigh.tmnsduc€rs. Box 2721 Stamford. J BLH Electroflics. DesiSn.PA 16127 rel:(412)458-96r0 PO.lnc.ai! gages. PA 189?6 tel:(215)343-041| faxj (215)343-7388 Div.Box338 Rr.MA 02021 rer:(6r7) 828-2500 42 nonhBenson Ave.Table7.Box I168 Uplnnd. Strain gages.croup 3624W LakeAveGlenvieqIL 60025 rcr:(84?)657-5300 P.CT 06906 tcl: (203)359-t660 tax: (203) 3s9-7807 3425Wald€nAve. lnc. Lord c€lh Testingmachinesand load Strain gagesand accassories Annealing fumrces Stresscoatsof ditrcr€nt All typesof straingages and relarcd acccssories for strain reading. Insa.of ffK FluidProd.lccessodes. SATECSystems. MTS SysrefisCorp. Lucifer Magnaflur Corp.NY 14043 tel:(7I 6) 684-000 I 900LibenySL OmveCiry. MI 48099 rel:(810)643-0220 fax:(810)643-0259 100RoyallSt. Canton. MN 55424 tel: (612)937-4000 fax:(612)9374515 65(14 EridgcPoinrR(|.NY 14217-1395 tel:(7l6)875-6240 faxr(?16)895-2404 75 Shawmu( Rd. NationalInsrumenG OMECA Engincering. Micro-Measur€menB D.on Inc.load cclls. and force Qu&rtztransducerstbr qua||(y m€asuremcnt Electro mechlnical (esling systcms Linear displacemcnr ltsting machincslnd . NC 276iI tcl: (919)36s-3800 telr(919)365-3945 www. Inc. PO. Dcpew. warringrcn.O. and all related acc€ssoriesfor reading.me:Irurcmen$group.prcssure.Inc.Inc.MA 02021 rer:(617)E2l-2000 fax:(617)828-145 | l?28 Maplelawn Rd. 2 mm andover 11500 1r 500 l0i 1otu Normalstatic lransouc€r servrcc: -75 1o+95oC !34c !1700 11500 100 l0? Normal: -75 to 205'C Special or sho(-term: -195 ro +260"C !29c r2000 1r800 t 1500 r0: r06 l0' r I 800 r 1500 t06 r0? -75" io +205'C ll09o for gagelengths undcr3.nexiblepolyimide lilm: high gate factorand extended fadguelife excellent tbr dynamicmeasuremenG.with a laminared polyimideoverlay lullr encapsuladng thegrid atldsolderrabs. and repeatable creepperforrnance.provided rv'lh largcsolderpadsfor easeof leadwire arrachment ' Fadguelife amproved usinglow-moduiussold€f.2mm t57o for 3. polyimide-filmbackjng.SVa i 1800 ir500 t0' Dynamic: -195 (o +205'C Normal: -195 ro + I75"C Spccialor short-Lcnn: -269 rc +205oC Normal: -269 !o +290"C Specialor short-term: -269 to +400'C ll. lrnd Bfld resistances. not nornally usedi|l slatic measurcments due to very high thermaloutputcharaclerisdcs Fully €ncapsulared gageswith high-cndurance isoelas!ic lecd wires:usedin wide-range dynamicskain measuremenl pplications in severcenvironments Equivllentlo WD Series.59e !2200 12000 t06 107 Noflnal: -?5 to + 120'C Speciirlor sho(-rcftn: -185 to +150'C tl.570 12500 12200 l0r Dynamic: -195 to +260oC Xl.rugged copper-coated tabs:primarilyusedfor general-purpose statjcrnd dynamicstressanalysis.imarilyrecommended for use in precisionrmnsdlcers.usedprirnarilyfor measuremenrs of largcposFyieidstrains.widestlemperature rangeandmostexueme cnvironmental capabilityof anygeneral-purpose gage wheoself-temperatu.) Gage Sed€s SA EP ED wt) SD Et SK Descriptlon and Primary Appllcaiion Telnperature Range Conslanunfoil in combinationwith a rough.wi!h large.'C'-featuregagesarc speciaU!.sarneusesasWA Series bur deat€dsomewhat in maximumtempcErureano opcratlngenvironment because of solderdots Normal: -?5 10+205"C Specialor short-te.rgessho$ zeroshift underhigh-cycjicsfains.J0 .oughoutthe gagelisrings Open-faced constantan foil Sageswith a thin.high-elongadon polyimidebacking.the N2A Seriesis charscrerized bf lo$.esrrictsfatiguelife ro Fully encapsulaled constaotan gageswith solderdotsl SamematrixasWA Series. Inc. primarilyusedwherea combinrion of hiSher slabilityat eievatedtemp€rature.c compensation is required. high-performance polyimidebacung.angeof optionsavailable.5% 13000 r2500 !2200 12500 t2200 1t800 105 l0r r03 l0o r0? 1U' tl.bul with solderdotsinsteadof K-lllor lbil in combioarionwirh a rcugh. Strain RanEe Fatlgue Lile Strain Level No. laminated.59o t2200 12000 l0o l0r Normal: -269 lo +230'C Specialor short-refin: ll.5Vononlinearat strain levelsoveri0.p. primarilyinbndedfor generalpurpose staticand dvnarnicstressanalysis:no! recommended for highesl accuracyransducers Universalg6n"o1-Or*osestraingages:constantan grid completelyencapsulaied io polyimide.but .2mm !5Eo tor 3.whercrheespeciallynai marix easesgage insrallation Fully encapsulated constanEngageswith hjgh-endurance Icrd rvires.5io I {. hithlightedth. of In p€ cycles Normal: -75 to +175'C Sp€cialor shoat-term: -195 ro +205'C l37o lor gagclengths under3.estrictelongationcapability) lsoclasdcfoil in combinarion with lough.availabl€wi(lj OptionsE. polyimidebacking.rn: -195 ro +230'C Speciallyannealed consrantan foil wirh tough.usefuloverwidertemperature rangesand in nrorcertremeenvifonments thanEA series:option w vailableon somepaftems. but restdctsborhfarigue lit! and maxiriumoperaringlompemture l_rullyencapsulated K-alloy gageswith solderdors:same usesia WK Series.ffexible. ' EPg. :rnd LE (may.2 mm rr800 r1500 1l 200 105 106 l0r Normal: -75 to +175'C Stackedrosetteslimiredto +65'C 1-lE fof Eagelengths under3.but d€ratedin maximumlemp€raluie und operatingenvironmen! because of solderdots -269' ro +260"C K-ulluy fbil laminaled!o 0. alsoaecommended lbr sressanalysisapplicalions employingla€e gag€ patEms.2mm t20% fbr 3. L.Table7.025-mm-!hick.Oplion W availableon someparrErns.3 StandardShain GageSerlesSelectionChart(CourtesyMeasuremenlscroup.2 mm r1000 t0b Dynamic: -195 to +205"C t2?o nonlineara( sllain levelsoveri0.5% lt.Rexiblepolyimidc brcung. grearesrbackingflexibiliryis required Fully cncapsulaled K-alloygages\rirh high-endurance lead wires.wide . This understandingis necessaryto make the bestoverall comPromisefor any Particular set of circumstances. less stable behavior.is the stockofgagesat While compromises hand for day+o-daystmin measurements. environment The cost of the strain gage itself is not ordinarily a prime considerationin gage selection. however. The sftain gageselectioncriteria consideredhere rclateprimarily to stEss analysisapplications. one of the shortestavailablegagesmight be the obvious choice. rational selection of gage characteristics and parameters caa be very important irl: optimizing the gage performance for specified envtonmental and operating conditions.and to judge the effects of that compromiseon the accuracyand validity of the testdata.the s[ess analystshould be fully aware of the effects of such compromises on meeting the requirementsof the gage installation. easeof installation . but quite the opposite is true. cyclic endurance . obtaining accurate and reliable strain measurements.contibutilg to the easeof installation. Procedu res.Recommendations . strain-sensitivealloy .The selectioncriteda for strain gagesused on transducerspring elements. t) accuracy stability temperarure elongation .At the same time. For example. gagepanem Basically.the selectionofa gageseriesor optionalfeaturewhich ilcreasesthe gagecost servesto decreasethe total installationcost. In many cases. options . of which the gagecost is usually but a small fraction. gdd resistance .This is becauseparameterchoices which tend to satisfy one of the constraintsor requiremelts may work against satisfying others. Another situationwhich often influences gageselection. Careful.0Introduction The initial step in preparing for any strain gage installation is the selection of the apPropriate gage for the task.125 in (3 mm) Ne geterally characterized by lower maximum elongation. are almostalways necessary. gages shorter than about 0. . It might at first appearthat gageselectionis a simple exercise..which are selectable in varying degrees: . reduced fatigue life. and the straingradientextemely high. backing materials (carrier) .the gageselectionProcessconsistsof determining the particular available combination of parameterswhich is most compatible with the envircnmentaland other opemting conditians. and minimizing the totdl cost of the gage installation. The MeasurementsGrcup's Transducer ApplicationsDepartmentcan assistin this selection. in the caseof a small-radius fillet. . where the spaceavailable for gageinstallation is very limited. MEASUREMENTS GBOUP ocopyrightMeasurements Group. The installation and operating characteristicsof a strain gage are affected by the following parameters. and greater installationdifficulty. self-temperaturecomPensationnumber .and leadsto compromise.of no greatconsequenceto the stressanalyst.sincethe sigdficant econornic measure is the total cost of the complete installation.l 1.t StrainGage Selection StrainGageSelection Criteria.Inc. gage length . These constraints are generally expressedin the form of requirementssuchas: r . It must be appreciatedthat the Processof gageselectiongen' erally involves compromises. may vary in many respedsto the considerationsPresented significantll from apPlicationto aPplicationand should be treated accordingly. ard at the same time best satisfies the installation and operating constraints. testdumtion .1989 .while similar herc. isoelastic(D alloy) offers certainadYantages. lette$ in the alphanumeric gage designation . the alloy is not in every casean indepeodently selectableParameter. of course. and causea correspondingzero shift in the strain gage.constantanis characterizedby good fatigue life and relativelyhigh elongationcapability. constaotan can be processedfor selftemperaturecompensation(see box at righD to match a wide rangeof test material expansioncoefficients.that constantantendsto exhibit a continuousddft at tempemturesabove +150'F (+65"C)i ard this characteristicshould be taken into accountwhen zero stability ofthe straingageis critical over a periodofhours or days.0 GageSelectionParameters AIloYs 2. when it is not necessaryto maintaina stablerefercnce PrinciPal zero . It must be noted.The S-T-Cnumber is the approximate thermal expansion coefficient in ppr/'F of the structural material on which the strain gagewill display minimum thermaloutput.P alloy is not ordinarily recommendedfor cyclic strain applications. or three. and its temperaturecoefhcient of rcsistanceis not excessive. that under high c)c&c stnins the P alloy will exhibit somepermanentresistance changewith eachcycle. Self-temperature-compensated (temPeraoutput designed to produce minimum thermal range over the temperature apparent strain) ture-induced from about -50' to +400"F (45' to +200"C). The thermal isoelasticalloy is included in output of uncompensated the samegraph for comparison purposes.1. compared to A alloy.Constantanin this form is very ductilel and.respectively. 0 3 . 0 6 .A alloy is supplied in self-tempemture-compensation ( S .This situation reflects the fact that comtantan has the best overall combinationof properties neededfor many strain gage applications. Self-Temperature ComPensation An important proPerty shared by constantan and modified Karma strain gage alloys is their resPonsivenessto specialprocessingfor self-temperaturccompenstrain gages are sation.1 3 .1. which is relatively insensitiveto stmin level and temperature.1 8 .It should be borne in mind.Micro-Measureform of conmentsA alloy is a self-temPerature-compensated stantan.integral leadwires.the thermal output cunes for A and K alloys (supplied with each packageof strain gages)do not apply. for example. 0 9 .however. 3 0 .or K-alloy gage is selectedto most closely match the thermal exPansion coefficieflt of the test material. and a high gagefactor (approximately3. among these are superior fatigue life. and still the most widely used. the thermal output curves for thesealloys can be lotated about the room-temperaturereferencepoint to favor a particular tempemturerange.annealedconstantan(P alloy) is the grid material normally selected. and the tendency for prematuregrid failure with repeatedstlaining. Micro-Measurements suPplies a variety of strain gage alloys asfollows (with their respectiveletter designations): form. the curve is rotatedcounterclockwise.An oppositemismatch producesclockwiserotationof the thermaloutput curve. however.That system is comprisedof a particularfoil and backing combinatioo. 0 5 .Cn) u m b e r s0 0 .2.the self-temperature-compensation (S-T-C)numbermust be specified. in gagelengthsof 0. A: Constantanin self-temperature-compensated P: Annealedconstantan.2 Isoelastic Alloy 2.or gagefactor. can be strainedto >207o.In addition.1 Constantan AlloY Of all modem strain gage alloys. However.and usually incorporates additional gageconstruction featues (such as encapsulation.This alloy has. 1 5 . the S-T-C number for an A.P alloy is ayailablewith S-T-C numbersof 08 and 40 for useon metals andplastics. Under conditionsof S-T-C mismatch.In normal practice.1Strain-Sensing The principal comPonentwhich determinesthe oPerating characteristicsof a sbain gage is the strain-sensitivealloy used in the foil grid. Wher' selectingeither constantan(A-alloy) or modified Karma (K-alloy) strain gages.that is.This is becauseeach MicroMeasurements strain gage series (identified by the first two.T . This is done by intentionally misrnatching the S-T-C number and the exPansioncoefficient in the appropriatedirection.an adequatelyhigh s[ain sensitivity. When the selected S-T-C number is lower than the expansioncoefficient. a modified Karma in form.125 in (3 rnn) and longer.see diaglam on page 1l) is designedas a comPletesystem. self-temperature-compensated The accompanyinggaph illusaates typical thermal output characteristics for A and K alloys.or solder dots) specific to the seriesin question. Very importantly. lts resistivity is high enoughto achievesuilableresistancevaluesin even very small gdds. n oC T E M P E R A T U RiE F F o J = UJ F TEMPERATURE IN 'F o . When purely dynamic strain measurementsare to be made . 2. of very largestrains. -2- For additionalinformatio[ orl sEaingagetemperature effects. K: Nickel-chromium alloy. D: Isoelastic.Becauseof this chancte stic.seeMeasurementsGroupTechNote TN-504. However.2) which improvesthe signal-to-noiselatio in dynamictesting. coNtantan is the oldest.5% (50 000t 8) or For the measurement above. 4 0a n d5 0 .and it will generallybe necessaryto calibratethe installation for thermal output as a function of tempemture. for useon test materialswith conespondingthermal expansiorl coefficients(expressedin ppn/'F). The individual backing materials are discussed here.3. 09. tbrm.the glass-fiber-reinforcedepoxy-phenolic backing material is the most suitabl€choice. Other propertiesof D alloy should also be noted when considering the selectionof this grid material. 06. SK. and ED-Seriesstrain gages. SA. . It is. or in addition to.the information on gageseriesperformanceand selectionis presentedhere. or. As in the case of the strain-sensitive alloy. In additior. WD.3 Gage Series alloy and As notedin Secfions2. the oPtion specifier).This table definesthe performance of each seriesin terms of operating temperaturerarlge.and where a fuIlbridge arangement can be used to achieve reasolable temperature compensation with.2 Backins Materials : Conventionaltbil strain gageconstructioninvolves a photoetchedmetal foil ptLtternmouatedon a plastic backing or carrier The backing servesseveralimportantfunctions: .and selection recommendationsare given in the table on page5.3Karma Alloy Modified Karma.As a rcsult.K alloy can be self-temPeraturc-compensatedfor use on materialswith differentthermal expansion coeffrcients.however.The specificstyle of copperteatment will be advised when the Customer Service Departmentis contacted.and cyclic enduranceasa function ofstain level. dependingon the availabletab area.ot serieJ. or K alloy. An inert atmosphere will improve stability and extendthe useful gagelife at high temperatures. Among its other advantages.efc)l that this alloy is not nor' mally usablefor static strain measurements. the high peel stength of the foil on the polyimide backing makespolyimide-backedgageslesssensitive to mechanicaldamageduring installation. 2. and thus permits rnore accurate correction for thermal output errors at temperatureextremes. for instance.r"n. its thermaloutPutis so high labout 80pe]"F (145p. For outstandingperformanceoyer the widest rangeof temperatLrres.the strain-sensing are not subject to completely independent material backing selectionand arbitrary combination.and given gageseriesdesignations. This a1loy is characterized by good fatigue life and excellent stability: and is the prefened choice for accunte static strain measurementsover long periods of time (monthsor yea$) at room temperanrre. however.includall general-purpose ing in eachcasethe alloy andbackingcombinationandtheprincipal constructionfeatures. but requires the specification of an available gage series.125 in (3 mm) or longer gage leneth.1. EP-.Cenain backing and alloy combinations.Like constantan. The duplex coPper featureis a preciselyformed copper soldedng pad (DP) or dot (DD).The availableS-T-C numbersin K alloy are limited. encapsulatedK-alloy strain gagescan be exposedto tempelaturesas high as +750'F (+400'C). in condensed The table on the following page gives brief descriptionsof Micro-Measuremenlsgageseries. to aid in understanding the properties of the seriesin which the alloys and backirg materialsoccur The Micro-Measurementspolyimide E backing is a tough and extremely flexible carrier. is now standardon all Micro-Measurementsope[-faced strain gagesproduced with K alloy.K alloy offers a much flatter thermal output curye than A alloy.With its easeof handling and its suitability for use over the temperaturerange from -320" to +350"F (-195'to +175"C). and its responseto strainis somewhatnonlinmagnetorcsistive. with its wide areas of application. lVK. K alloy is the normal selectionwhen a temperature-compensated gageis requLedthat hasenvironmentalcapabilitiesandperformancecharacteristicsnot attainablein A-alloy gages.that the performancedataarc nominal. as the alloys were in the prcvious section.becomingsignificandy so at stminsbeyond t5000pre. the backing is not completely an independentlyspecifiable pammeter. Due to the difficulty of soldering directly to K aUoy. Reinforcedepoxy-phenolic backing is employed on the following gage series:WA.in the ckcuit. It is recommended for extended static sfain measurementsover the temperaturerangefrom -452" to +500'F (-269" to +260'C).All K-alloy gageswhich do not have leads or solder dots are specif. however. where eachseriesgenerallyincorporatesspecialdesignor constructionfeatures. provid€sa meansfor handling the tbil patternduring installation al . 13. . the processdoes not permit the a$irary combination of an alloy ard a backing material.2.There are times.a$d apply primarily to gages of 0. however. For short periods. ear.1 ar'd2.For conveniencein identifying the appropriate gageseriesto meet specifiedtestrequirements. in rwo tables.OpenfacedK-alloy gagesmay also be orderedwith solder dots. In short-term applications. 03.lnstead.Polyimide backing is a featurc of Micro-Measurcments EA-. and can be contoured readily to fit small radii. 05.D alloy is not subject to self-temperaturecompensation. Each serieshasits own characteristicsand prefened areasof application.Micro-Measurements gage s€ries artd their ProPertiesare describedin the following Section2.which was formerly offered asan option. represents an importaot member in the family of strain gage alloys. provideselectricalinsulationbetweenthe metal foil and the testobject -3- Backing materials supplied on Micro-Measurementsstrain gages are of two basic types: polyimide and glass-fiber-reinforced epoxy-phenolic. SzK-. and SD.and can be usedto measureplastic strainsir excessof 20Vo.are designedassystems.a selectionmust be made from among the available gage systems.to about 1 to 2%. Moreover. the upper temperaturelimit can be extendedto as high as +750'F (+400'C).straio range.or Iesserperiods at elevatedtemperatue.. The maximum elongationof this carrier materialis limited.redwith DP or DD as paft of the designation(in place of.This backing is capableof large eloogations. when D alloy finds application in special-purpose transducerswhere a high output is needed. and 15.It must be noted. when arriving at the optimum gagetype for a particular application.as well asa specificcombinationofalloy and backing material.to the followirg: 00. This backing can be used for static and dynamic strain measulement from -452' to +550'F (-269' to +290"C). 2. a readily bondablesurfacefor adheringthe gageto Lf the testspecimen . EK-. CEA-. polyimide is an ideal static and dynamic stess backing materialfor general-purpose analysis. .the duplexcopperfeature. N2A-.asshown in the graph (seebox). 2.along with specialconstructionfeatures. and LE (day reslrictelongation r'1800 11500 *240 !2'h NOrmat: -452. L.llexiblepolyioil in combination lsoelastic imidefilm.Wide rangeof optionsavailable' static and Friinarilyintendedfor general-purpose fgr highest analysis.Usedprimarily withOplons Availab'e strains.5% !2400 !2240 i2000 10" 107 '10" !1. measurement aoplications Dynamic: -320' to +500'F (-195' to +260'C) t1.Providedwjth largesolderpadsfor ease of lead(-185" to +150"C) v\.Io +!tu-l- (-269'to +290"C) Specialor Shoft-Term: -452' lo +750'F (-269" to +400"C) Normal:-452" to +450"F K-alloygageswith solderdois. underhigh-cyclic withtough. !3'/" lot gage 11500 1oo lengthsunder 118i^ (3. :RTES i . in slaticmeas. ients of largepost-yield capability).StandardStrainGageSeriesSelectionChart :.with a laminated Specialor Short-Termr the grid and solder imideoverlaylully encapsulating -300' io +300'F tabs.2 nn) i5% for 1/8in and over !3"/. Fullyencapsulated (-269" to +230'C) temin maximum derated Series.001in (0.5Y" r22OO 12000 10' 107 t1800 r1500 10" 107 to WD Series.iomnal.57o. WK 108 LA6tal -100"to i4oo"F Normal: constantangageswith solderdols.andapplyprimarilyto gagesof 0 l 25-inf3-mmrgagelengthor larger' -4- .high-elonSoeciallvannealedconstantan for measureqition potyirnid" backing. E..fleJible' folyimidebacking. Fullvencapsulated (-75" to +2o5ec) WA Series uses as Same same matiixas WA Series.2nm) !20"/" tot 1/8in anoovea !1000 10- EP gagesshowzeroshift sirains. gage oi any general'purpose capability envirormental i s r e q u ired c o m p e n s a t i o n w h e ns e l f .but restrictsboth tefl'perature fatiguelifeand rax'mumoperating !1.5% a1800 107 K-alloygageswith high-endurance Fullyencapsulated rangeand mostexreme Widesttemperature leadwires.mallyused excellenlfordvnamicmeasurements. -100' to +250"F Normal: to 0. andover usinglow-modulus -100"to+4OO'F Normal: (-75' to +205"C) Specialor Short-Terrn: -320' to +500'F (-195'to +260"C) foilwithtough.Not recommended dynamic-stress accuracvt€nsducers. encapsu oridcomolelelv usedfof generaltabs Primarily iuooedcoooer-coated 'c'-Feature analysis stress dynamic and siatic ouiiose gagelistthe throughout highlighted gagesarespecially ingsoJCatalog500. Dynamic: -320" to +400"F (-1ss" to +205'C) at Nonlinear strainlevels overr0.2nm) 'Fatigueliie imp. -100' to +350'F Normal: (-75" to +175"C) Stackedrosetteslimitedto +150'F(+65'C) NormalStatic Transducef Service: -100'to +200'F NZA /-746 h StralnIevel Numbet ln pe of Cycles i3% lor gage lengthsunder 1lAin P. rA. High gage factorand extendedfatiguelife Notno.t e m p e r a t u r e OptionW availableon somepatterns.butwithsolderdotsinsteadof Equivalent leadwires. Normal:-100" to +350'F (-75' to +175"C) Specialor Short-Term: -320" to +4009F (-195" to +205"C) straingages Constantan Universalaeneral'purpose atedin poyimide'with iarge. 1l8 n (3.oved i5% for 1/8in solder.ireattachment.5% See above note 12500 !2200 10" to +350"F Normal:-320" with a tough.arilyusedwhefea combination imide'backing.nonlinearat strain levelsoveri0. Specialor Short-Terml highergrid resistances.025mm)thick.5% !3000 12500 12200 10" 107 108 Dynamic: -320' lo +400'F(-195" to +205'C) i1.5% 12500 \2200 10" 107 gageswilh high-endurisoelastic Fullyencapsulated ance leadwires. APPLICATION ANDPHIMARY DESCRIPTION . Specialor Short-Term: and but defatedsomewhatin maximumtemperature -320'to +450"Ff-l95" to +230"C) becauseof solderdots.flexiblepolyK-alloyfoil in combination (-195" to +175"C) of Prir.Usedin wide-rangedynamicstrain in severeenvironments. WD !1700 a1500 12000 a1800 a1500 -100'io +400'F t^ !rn6oC) 10" t06 107 +1800 !1500 i10% forgage lengthsunde. operatingenvironment t-7cd 1o: 10" i1500 10:.rementsdueto very highthermal-output characteristics. but as WK Sameuses Specialor Short-Term: peratureand operatingenvironment becauseot solder -452' to +'oO"F (-269" to +26A"C) dots.andqreatestbackingflexibilityare required !1. n€ :)riormance datagivenherearc .highK-alloyfoil laminated (-75" to +120"c) polyperformance polyimidebacking.stabilityat elevatedtempera-452" lo +4oa"F(-269" to +205'C) lure. FATIGUE LIFE RANGE TEMPEFATURE 6o*t"nt"n foil in combinationwith a tough. .-"6i.HAI9E t l Maximum Number Strain.accuracy" li is inappropriate 'very high"1% or ior stressanalysispurposesis in the 2 to 5% range.and correspondirglyaf'fectsthe performanceof the gage. SK.) typeofstrain measurement gage of installation temperature operating test dtfarion acculacyreqlLired required cyclic endurance This tableprcvideslhe basicmeansfor preliminary selection 1 of ... . thefollowingctiteria: ' ' . SA 610 <104 Eener|han 0. WA./4€ ot Cycles Moderate <10" -50: to +1so'F (-45' to +65'c) STATICOR STATIC.Strain GageSeries and Adhesive SelectionFleferenceTable cYcLlc REO'D ENDUHANCE 'opesnttNc ' j TEMPERATUHE .tr.In suchcases.5% i1600 10" WA. DYNAMIC 11300 r'10" 11600 -50' ro +4OO"F(45d to +205'C) High <103 ' ANALYSIS- High AE-10or AE-15 <10" AE-15or 610 !2000 >10- AE-15or 610 *1600 <106 600or 610 12000 <106 600or 610 610 *2000 >103 <10 11800 <106 !1500 <106."or setsof testrequirements.F {+65"q.. thatis beyondtheranges Whena testprofileis encountered that the specitiedin the abovetable. i1800 10" WK.50/. it may be necessaryloomployhalf-or tull-bridgecon' . ' . The abovetable giveslhe recommendedgageseriesfor speby categorized cific test"profiles.".2% <106 -50" to +30O'F (45" to +150"C) M-Bond Adhesive 200orAE-J0 i1300 rl oa I r10a GageSeries slabilitywith Thls cateoorvincludesmost testinqsifuationswheresome degreeof slabilityunderstatictest conditionsis required.&. 'i'.!"o.This selectiontable.The proin Sectron3'0 of this thisis described ceduretbr accomplishing Tech Note.ries for most conventionrlapplicationsh rlso f includesrecommendirlion sincethe adhesivein s lbr ildhesives. r1300 <106 +1500 10' N2A 600."high"in the 1 to 3% range.and rn"ni"iioii . .it can usuallybe assumed approachor exceedthe performancelimitxtest rcqLrireDlents tions of availabiegages.1O i50 000 1 >109 a" b +5o0'F(10'to +260'C) >103 l\.For absolule above+150.2 to 0.610 rc1 2OOor AE-10 DYNAMIC (cYcLrc) ANALYSIS -320'to +500'F (-/95" to +260'C) <104 610 Moderate 12400 107 WD lvloderate 12000 107 WD Nloderate i2300 <10' WD 600or 610 1lo5% +1300 <10" CEA. a strain gageinstallationbecomespart of the gage system. is herrnetically figurations. is used in conjunctionwith Cataiog500' Ptecision StrctitlGqgesto aftive at the complategageselection.SK 610 -.the complexfor presentation EngineeringDePartment Applications usershouldconsultthe in arriving at the besf for assistance of Micro-Measurements compromlse. | L (static. gages.dynamic.. AE."moderat6" befter...s .6'10or 43-B <1oo 0.etc.50"ro +2O0'F(45" to +95'C) -320" to +350"Ff-79. EA AE-10or AE-15 AE-'l0or AE-15 1 to 5'l.Under theseconditions'the interactionsbetweengage performancechamcterislicsbecometoo in a simpletable.suppiementedby the information in the tableon -5- page 4..Fr6tectivecoaiiigs may also inituencesiab'lityin cases otl'er than transducerapplicaliorslvhere Ihe elemenl and the instruas used in this tablewithoutconsideralionofvariousaspectsol the aclualtestprcgram to quantify. rongpeiioot ot usage and temperatJre.5'to +175'C) SA. WK Beter t'ran 0.lri -qJnerat.4oderate +200000 1 <102 Moderate 115 000 1 t10 000 1 600o. flexible gagescan be conoured to almost any radius.atively large cross-sectionalareaand low electdcal resistance. Strain gages of less than about 0 .for example.Becausethe useof a small straiDgagemay introducea number of other problems. lower wattageper unit of gdd area. backing.resistanceto damagein handling.the Micro-Measurcments it (0. 0.For are usuallymadeat the most critexample.Considerconcrete. large gages provide improved heat dissipation becausethey introduce. and testspecimensurface. In overall handling characteristics. Still anotherapplicationof largestrain gages.convenience.sfain measurements ical points on a machinePart or structure.the highly stressed points are associatedwith sftess concentrations.the stability under static strain.5 ]n ( 13 mm). and demonstratesthe error in strain indicatedby a gage which is too long with respectto the zone of Peaksfain. very commonly.And.2 mn) to -. When they can be employed. Since the average of any nonuniform strain distdbution is always less than the maximum.it is oftefl necessaryto compromrse.that is.1 times the radius of a hole. the CEA Series is usually situations' the preferredchoice for routine strain-measurement capaenvironmental or in extremes iequiring Performance not gage or lengths.The endloopsand solder tabsare consideredinsensitiveto strainbecauseoftheir rel. for examPle. this rule of thumb can lead to very small gage lengths.As indicated in the previous table. or notch.thi gage(photographbelow).say.or avenge. The strain gagetends lo integrate. often very large gages. etc.Division offers gagelengthsrangingfrom 0 0Q8 ( mm). o Jr€ 2. fillet. When any of theseconsiderationsoutweigh the inaccuracy due to strain averaging. They are usually easierto handle(in gage lengthsup to.This considerationcan be very important lvhen the gage is instaltedon a plastic or other substratewith poor heat transfer Properties lnadequateheat in the grid.in this case.for the same nominal gage resistance. at the most highly stressedpoints. CEA-Series gages are oqtstanding. A-alloy gages. Thesethin.5 in or I3 mm) ir nearly everyaspect of the installationand wiring procedurethan miniaturegages.4 GageLength The gagelength of a sfiain gageis the activeor shain-serlsitive length of the grid. a strain gage which is noticeably largerthanthe maximum strainregionwill indicatea strain magnitudewhich is too low.larger gagesoffer several advantageswofth noting.When mea- @ . Optimiiing Strain Cage ExcitationLevels).is in saain measurementon nonhomogeneousmaterials. the gagelengthshould be no greaterthan 0. where the stmin gradientis quite steePard the areaof maximum strain is restrictedto a very small region. say.adhedissipationcauseshigh temPeratures sive. 4 in 100 As a rule of thumb. or the correspondingdimension of any other stressmiser at which the strain measurementis to be made.and may noticeablyaffectgage performanceand accuracy(see MeasurementsGroup Tech Note TN-502. rvhenpracticable. the strai[ over the areacoveredby the grid.125 irr (3 nn) gagelength performance-Particularly in termsof tend to exhibit de-sraded the m&\imum allowable elongation.featuringlarge' rugged' oolyimide-encapsulated tabs for ease in soldering leadwiresdirectly to "oooer-coated -. The sketchbelow illustates a representativesftain distribution in the viciflity of a shessconcentration. and endurance when subjected to altemating cyclic sftain. bilitiei (and not requiring the very srnallestin gages are suain CEA-Series " specializedgrid configurations)..0.Vy'ithstless-miser configurationshaving the significant dimensionless than.a largergagemay be requircd GAGE LENGTH K ffifi[illilXiilil Irl Gage length is often a very imPortantfactor in determiring the gage performanceunder a given set of circumstances. as shown below. Furthermore.which is a mixture of aggregate(usually stone)and cement. To satisfy the widely varying needs of exPedmental stress analysisand transducerapplicatioos. suring strainsin a concretestructureit is ordinarily desirableto usea strain gageof sufficientgagelength to sPanseveralPieces of aggregate in order to measurc the representadvestrain in the structure. gradient perpendicularto the test surface(as in bending)' the single-plane rosette will produce more accurate strain data becauseall gdds are ascloseaspossibleto the testsurface.a threeelement rosette must be used to obtain the principal saessmagnitudes.typically 120 ohms vs.the single-planerosetteis in terms rosette superiorto rhestacked of heattransttrto the testsPecimer.In certain instances.25i\ (3 to 6 mn) are preferab\e. degree (or "tee") rosette can be ernployed with *re gage axes aligned to coincide with the principal axes. 2. when the foregoing considerations do not dictate otherwise. when there are large strain $adients in the planeofrhe testsurface. as in a cylindrical pressurevessel.a comstrain meamon casenecessitating three-element a twoor surcment rosetteis requiredin orderto determinetheprincipals[esseswhen the directionsof the princigalaxesare 90a two-element knownin advance.It is alsoimportant that the tab anangementbe such as to not excessivelytax the proficiency of the installer in making proper leadwireconnections. StackedroseEe generallyproviding betterstabilityand accuracyfor staticstrain Furthermore.the only difference betweentwo gagepattemsavailablein the sameseriesis the gdd resistance. while shorter gages are usually inferior in these characteristics.the single-plane rosettecan produceenors in stnin indicationbecausethe grids samplethe strain at differentpoints For theseapPlicationsthe stackedrosetteis ordinarily preferable.For example.when the dircctions of the principal axes arg not known ftom other considerations. larger or smaller sizes generally cost more.The largest selection of gage pattems and stock gagesis availablein this range of lengths.particularly when the gage is to be installed orl a material or specimen with poor heat transferproperties.when there is a significant strain measurements. 350 ohms. shouldalways carefulconsideration be given to the differencein characand single-plane teristicsbe{rveen For any givengage stackedrosettes.and variousconstructioflfeatures which are standardfor a Particularpattem. or other sources of random resistancechange.5 Gage Pattern For a biaxialstressstate.and failure to considerbiaxiality of the saessstatecan lead to large errors in the stressmagnitudeinferred from measurementsmade with a single-grid gage.but is usually gdds is of the that one so mounted -7 aligned with some significantaxis of the test object.axes are obvious from the symmetry of the situation. I With single-grid gag€s.ofcourse. the gage length should normally be large with respect to the dimensions" of the inhomogeneities in the material. and unwantedsignal variations causedby leadwire resistancechangeswith temperaturefluctuations' Similarly. the samePower In experimental stress analysis.The usual 6o-d"sr. stability. length.the higher-resistance generation rate by a factor of three heat that it reducesthe (for the sameappliedvoltage acrossthe gage). All details of the grid and solder tab configuradons arc illustrated in the "Gage Pattem" columns of Catalog 500.not the seYetelocal fluctuations in strain occurring at the interfaces between the aggregate Partl' cles and the cement. The wide variety of pattems in the list is designed to satisfy the full range of normal gage installationand srain measurementrequirements.The stackedrosetteis also advantageouswhen the spacefor mounting the rosetteis limited. when measuring stlains on structures made of composite materials of any kind. When gageis preferablein the choice exists.d width -When severe strain gradients Perpendicular to the gageaxis exist in the testspecimensurface. In other words. On the orher hand.asis often the case.be compatiblein size and orientationwith the sPaceavailableat the gageinstalla' tion site. Three-element rosetlesare available in both 45degree rectangularand 60-degree delta configurations. the number and orientationof the grids in a multiple-grid gage' the solder tab configuration. it is usually the aver4ge strain that is sought in such instances.The rosettecan be installed 45-degree rosette with any orientation.the shapeof the test object and the modeofloading may be suchthat the directionsofthe principal . Gri. when available and suitable to the installation site.a nafiow grid will minimize the averagingerror Wider grids. will improve the heat dissipation and enhancegage stability .h *!46- <ffi> Whena rosetteis ro be emPloyed. The gagepattem refers cumulatively to the shapeof the gdd. and larger gages do not noticeably irnprove fatigue life. tf go-degree rosette Gage resistance. ff.sliP rings. rosen" choice is the rectangularrosette since the data-reductiontask is somewhatsimpler fot this coflfiguration. Furthermore.ertabs-These should. gage lengths in the range from 0. The dircctions of the principal axes can sometimes be determined with sufficient accuracy ftom one of several considerations. when the gagecircuit incltrdesswitches. pattem suitability for a particular applicationdependsprimarily on the following: Sold.Still anotherconsideralionis that stackedrosettesare genemlly less conformableto contouredsurfacesthansingle-planerosettes. As a generally applicable guide. In genelal. or elongation.The princiPal axes can also be definedby PhotoStress-testing. a single-grid gage would normally be used only when the stJessstate at the Poitrt of measurementis known to be uniaxial and the directionsof the Principal axesare known with reasonableaccuracy(15") -7 - In the most generalcaseof surtr/4\'1 face stresses.the signal-to-noise gagesoPeratingat ratio is improvedwith higherresistance level.These requirementsseverelylimit the meaningful aPplicability ofsingle-grid straingagesin stressanalysis. ..125 to O.Higher gage resistancealso has the advantageof decreasingleadwire effects such as circuit desensitizationdue to leadwire resistance. Supplementaryprotectivecoatingsshouldstill be appliedafter lead attachmertin most cases.025mm)l thick. Staldard options are notedfor eachseosorin Catalog500. Grid Protection: Entire grid Fatigue Life: When gagesare properly wiled with smalljumpers.with littie sacrificein flex10.Option E protectsthe grid from fingerprints and other contaminating agentsduring installationand. ED. lncreasedreliability of applications r Simplified installationof sensorsin difficult locationson comPonentsor in the field . -8- . Increasedprotection.Temperature Limiti No de$adatioo. therefore. Reduction the skill level necessaryto make depend' able installations - .tional rcirforcement of the polyimide encapsulation can cause bond failure before the gage reaches its full stuain capability. Achievementof specialperformancecharacte stics Standardcatarogoptions o IntegralTerminalsand Encapsulation Option 17 SeriesAvailability:EA. EK.both in handlingduring installation and shieldingfrom the test environment .Heavier leadsmay be attacheddircctly to the gagetabsfor simple staticload tests.6 Optional Features offersa selectionof optionalfeatures Micro-Measurements - for its strain gagesand specialsensors.ResistanceToleranc€: Resistancetoleranceis normally doubledwhen Option E is selected. f.The addition of options Availability of each option varies with gage seriesand paltem.sinceno intemal leadsor solderale presentat the time of installation.'' 2.Strain Range: Strainrangeofgageswill be reduced because. enduranceis easilyobtained. EB WA. Solderingis $eatly simplified sincethe solderis preventedfrom tinning any more of the gagetab thanis delibirately exposedfor lead altachmeut. Shown below is a summaryof the optional featuresoffered.Q01 ibility.:::ffil:1?:JiTffi'nH:1ilffii::esthecost'butthis - r Significantreductionof installationtime and costs -of . maximum andpart of tabsare encapsulated.contributessignificantlyto long-term gagestability.the addj.ED' WD. EP General Description: Option E consistsof a protectiveencapsulationof polyimide film aPProximatelyI mil n (0. EK' WK OptionE SeriesAvailability: EA.Size: Gagesizeis not affected. This providesruggednessand excellentgrid protection. Flexibilityr Option E gages arc aknost as conformable on curved surfaces as open-facedgages. (+2?0"C) rin-silver tons. ED. EK' EP OptionlE SeriesAvailability: EA. It also contri^butes greatly to inviionmental protection. but with the addition of a i-mil 10.Opiion of OptionLE' addition the reducedby usually be rarge will Strain Range: Strain is uncianged. the specimensurface. Fatiguelife will normally be degradedby option gages suchas the ED Senes.FatigueLif€: the leadwires and between uncoveredat the leaclwireend to preventcoltact the copPerribbon has. Resistance as standard as conformable are not LE with Option Gages Fledbiliiy: toleralce is oormally doubledby the addition of Option LE. -9- . EP Optionl. ED. SeriesAvailability: EA.025-mm)lthick encapsulationlayer of polyimide film. Leads are approximately0-8 in (20 mm) lorg. Grid Protection: Entire gageis encapsulated.F (+)b0"C). EK' EP I U U General Description: ThJsoption providesthe sameconlormablesoft copperlead ribbonsi-c usediu oprion L. Solder: +430'F A shortextensior of the backingis left Limit: +400.Option 5E SeriesAvailability: EA.A good part of the reasonfor this is that the encapsulationlayer Prcventscontaminationof the'grid surfacefrom fingerprins or other agentsduring handlingand itstallation.30 x Temperature alloy. The presenceof suchcontamcominantswill causesomeloss in gagesrability.limitprimarily because This occurs LE.004 in thick(0. The encapsulation layer provides excellent protectionfor the gage during handling and installation. Size:Matrix size Resistance Tolerance: gages.thoughsupplementarycoatingsare still recomrnendedfor field use Gages ivittr Option lf wiil normally show betterlong-termstability than open-facedgageswhich are "waterproofed" only afier installation. EK. ED. high endurance for very often recommended LE is not ed c"yclicendurance.Leads: Nominal ribbon sizefol most gagesis 0.012wide x 0.even thoughthe gageis subsequentlycoaredwith protective ribmm) copPel 0 10 pounds.001-ir(0. optionsL andLE' Thegenorientationof leadwires showthestandard Theseillustrations also apply to leadwireorientationfor -i" ir .frut tfr" f"adsale Pamllelto the longestdimensionof the Pattem.in strainmeasurcmentfor stressanalysis.l0- o .and superiorfatigue life. of the CEA Seriesaregiven in the correspondingcharacteristics the right-mostcolumn of the table' It shouldalsobe notedthat many standardstraingagetypes' without options.Comparing.-.are normally availablefrom stock.the choice of options ordinarily involves a vadety of comPromises.7Characteristics Gages OPtionson EA-Series As in other aspectsof strain gage selection. the informatior supptiedin this section is directed primarily toward such option applications. the respectiveperformancePanmeters for an open-facedEA-Seriesgagewithout optionsare arbitarily assigneda value of 5.forexample.whenthepatternshownis available *. For instance.the standard options are most frequently applied to EA-Series strain gages.The illustrations these series' one of in "i^i WX. In the table below. Numbersgreaterthan 5 indicatea Particular parameteris improved by addition of the option' whiie smallernumbersindicate a rcductionin Performance. the first considerationshould usually be whetherthereis an equivalentCEA-Seriesgagethat will satisfy the testrequirements.q.LeadwireOrientationfor OptionsL and LE relativeto thegagepaftemgeometryfor. oo nI A tl IJLJ U |rl TTT JI EE (3 or 4 tabs) TI trE OnO TTTT TTTT TTTT TT When contemplating the application of an EA-Series gage with an option. it will be found that the latter is characterized by lower cost. OPTIONS STANDARD ATTHIBUTE INSTALLATION PARAMETER OH PEHFORMANCE '10 LE E L 7 5 10 10 l' 7 7 7 8 a I 4 3 3 .For comparisonPurposes. of StandardCatalog 2.Becauseof the many interactions between installation attdbutes and performance parametersassociatedwith the options' the rclative merits of all standard options are summadzed qualitatively in the chart below as an aid to option selection.while gages with options are commonly manufacturedto order.an option which maximizesa particular gage performance parameter such as fatigue life may at the same time requiregreaterskill in installing the gage. an EA-Series gage equippedwith Option W and a similar CEA-Seriespattem.^naWp-seriesgages. The only possibleadvantagesfor the selectionofOption W are the wider variety of availablepattems and the occasional needfor largesolderingterminals. and may thus involve a minimum order requirement. Since.grcaterflexibility andconformability. If this combinationis not listed as availablein the catalog. there are often advantagesfrom selectingthe 350-ohmresistanceif this resistanceis compatible with the instrumentationto be used.This decision may be influenced.particularly in the caseof very small gages. and listed in order of size.canalsobe selectedfrom a number of different grid and solder tab configurations. ifany).it is wise to selecta gagefrom the SuperStock Listings to eliminate the likelihood of extendeddelivery time or a minimum order requfement. which gives the recommendedgage seriesfor specific test "profiles". or setsof test requirements. of cou$e.With three-elementrosettes(rectangularor delta).Quite frequently.The gage and its solder tabs are large enough for relatively easy handling and installation. These are: the gage series.^ .it may be necessary to select a[ alternate series and rcPeat this process.This section should always be rcviewed first to locate all aPpropnategage. (b) improved strain averaging on inhomogeneous materials such as frber-reinforced composites. the S-T:'C number. the gage length and Pattern are normally the fust and second selections to be made.a similar gagepattem in the same size grouP. As notedunder the gagePattemdiscussionon page7.^ ^ A ruwurts P44Er4yu. Qn the other hand. A good starting point for initial consideration of gage length is Q-125in (3 nnL This size offers the widest varieiy of choices from which to select remaining gageparameteff such as pattem.The sameis true. as describedin Sectrbz 2.it is evidentthat therea-rebut five parametersto select.Some reductionin fatigue life can also be expectedfor the high-res. series and resistance.a shortErgagelesgth may be oecessarywhen the object is to measure Iocalized peak strainsin the vicinity ofa stressconcentration.In thesecases. or (c) slightly easier handling and installation [for gage lengths up to 0.however. At the same time. :.the Srain Gage Selectior Checkliston page 12 shouldbe refened to as an aid io accountingfor the testconditions andrequirementswhich could affect the selection' . . Single-grid gages are available with different asPect for (lergth-to-width) ratios and varioussoldertab arrangements adaptabiiityto differing installationrequirements. reference is madeagain to Catalog 500 to lecord the gagedesignationof the desiredgagesize and pattem in the recommendedseries. Of the preceding parameteff. when the spaceavailable for gagemounting is very limited.3. The principal reasonfor selecting a longer gage would commonly be one of the following: (a) greater grid area for better heat dissipation. -lt- With an initial selection of the gage size and Paftemcompleted.the option shouldbe tentatively specified at this time. Despite the large number of variables involved. This completesthe gageselectionprocedure.by cost considerations. In selecting the gage pattern. The strain gages in the SuPerStock sectionof the catalogare the most widely used for stress analysis applications. and especially for routine stoainmeasurement.not counting options. Micro-Measurements offers a great variety of gage tyPes for meeting the widest range of strain measurcmentleeds.0 GageSelectionProcedure I The performanceof a strain gagein any given applicationis affected by every element io the design and manufacture of the gage. After selectingthe gageseries(and option. and any other features common to the series.istancesmall gages.5.50 in ( 13 tnn)1. ^ ^ . is between planar and stacked construction. .can usually be selectedfor meeting the installation and test requircments'In exheme cases. based on the space available for gage mounting and the nature of the sEessfield in terms of biaxiality and exPectedstrain gadient.5). the first consideration is whether a single-grid gage or rosetteis required (seeSection 2.In eachstepof the procedure.This is accomplishedby referring to the chad on page5. Similar pattems available in each gage length are grouped togethe!. the S-T-C number should be insertedfrom the list of availablenumbers for each alloy given on page 4 of catalog 500.when applicable.Two-element 90-degreerosettes. gages of this length provide performance capabilities comparableto thoseof largergages.the next step is to selectthe gage series.If the gage seriesis to have a standardoption applied.From the diagrambelow that exPlainsthe gagedesignationcode.Finally. U The format of Catalog 500 is designed to simplify selection of the gage length and Pattern.such asa hole or shoulder. the process of gage selection can be reduced to only a few basic stePs.morc than one gage size and Pattem combination will be suitablefor the specifiedtest conditions. or a slighdy different size in an equivalentpattern. . the gage length and pattem. in recording the completegagedesignation..and the resistance. since the availability of the desired option on the selected gage pattern in that series requires verificatioa durin-g the Procedure outlined in the fol' ^ .thus determining the foil and backing combination.once the gage length has been determined.the primary choice in pattem selection. GagePanenof the principal axes are obvious from considerationsof symmetry. FOR CONSIDERATIONS PARAMETERSELECTION Y Selection SteP: 1 Paameter: Gage Lenglh Selection SteP: 2 Panmetea: Gage Pati'ern Selectian SIep: 3 Paameter: Gage seties tr E E I E E E E E straingradients strain areaol maximum accuracyr€quired staticstrainstability elongation maximum cyclicendurance heatdissipation spacelor installation eas6of Installation tr tr tr tr tr (in"Plane straingradients andnormalto surface) ol stress biaxiallty heatdissipation spaceforinstallatlon easeof installation availability gageresistance tr tr tr tr u Parametelr Gage Resistance E tr Step:6 Seteclian Parcneter S-1-cNumbet o A. three examples are given of the gage-selectiort procedurein representativestressanalysis situations. simultaneously keeping in mind the test corditions and environment. and the test requirements.Very short gagelengthsshoutdbe avoided in order to minimize heat dissipationproblems causedby the low thermal conductivity of the plastic.25-in (6. however.0 GageSelectionExamPles 4.3-nn) gage length is specified. The model is quite large. Whether formally or otherwise. bone. becausethe widest selectionof gagepattemsis availablein this length. the knowledgeable practitioner does so in the light of parameterselection considerations such as those itemized in the preceding checklist. tbe 250BF patternis a good compromisebecauseof its high grid resistancewhich will help minimize heatdissipationProblems.room tempemture. the directions 2. forces. Instead.atrdthe like. the gage installation constraints. In someareasof the model.anddo not embraceexoticaPPlications centri.rapid meansfor of thetestProhelpingmakecertainthatno criricalrequirement It should gage is overlooked' selecdon affect could hle which "considerations" that the the checKist in using in mind bebome listed apply to relativelyroutine andconventionalstressanalyinvolving sissituations. a 0. and apparcnllyfree of severestrain gradients. etc. E typeof strainmeasurement (static.5.and single-gridgagescan be employed.) dynamic. therefore. dynamic. It should be noted. post-yield.atio signal-io-noise material tr testspecimen range temperature tr operating tr accuracyrequrreo Gage Selection: L GageLength.The model will be testedstatically at.fugal exfteme nuclearradiation. individual tests will take only a few hoursto run. Design Study of a Pressure Vessel are to be madeon a scaled-downplasStrain measurements tic model of a pressurevessel.Of the pattems aYailablein the selectedgage length. etc.and. or near. environment installation gr field laboratory requkements stability of sensitivity solderihg (Plastic. typeof measurement {static. -12- o .An attempt has been made to provide the principal reasons for the particular choices which are made. the analyst reviews Catalog 500 and quickly segregates the more likely candidates from among the available gage-pattem and series combinations in the aPPropriate sizes' The selection criteria are then refined in accordance with the particular stain-measuement task to convelge on the gage or gagesto be specified for the test Progam. althoughthe testsmay be conductedover a period of severalmonths. application post-yield.intensemagneticfields.0 Strain Gage Selection Checklist This checklistis providedas a convenient. that an experienced streasanalyst does not ordinarily proceed in the same step-by-stepfashion illustrated in these examples.) E operatingtemperature E testduration E cyclicendurance required E accuracy E easeof installation Selectlon Slep: 4 Paftmeter: Oplions Selec on SIep: 5 In this section.etc.) substrate forinstallation spaceavailable timeconstraints installation heaidissipation desensitization leadwire . the 250RD Pattemis a good choice.a particularly thin gageinstallationmustbe made. Catalog 500 lists the rcsistanceas 350 ohms. Gage Series-Low strain levels are expectedin this application: and. 3. the 03lCF pattem is chosenfor the task.Because the gear is a spur gear.e. AnticiPating Problems which would otherwisebe encounteredin Steps2 and 3. The selectedgageresistanceis thus 350 ohms. Gage Paftem ." GageDesignation: the theresultsof the aboveselectionprocedure. Becausethe gagemust be very flexible to conform to the small fillet ndius. Option L (prcattached leads) is therefore selectedso that the instrument cable can be attached direcdy to the leads without the application of a soldering iron to the gage proPer.since a stackedrosette would contribute significantly to reirforcement and heat dissipatiorl Problems.but referenceto Catalog500 indicatesthat such a choice severelylimits the availablegage pattems and grid alloys.Isoelastic (D alloy) is preferred for its higher gage factor (nominally 3. the dircctions of the principal axes are known. 4. S-T-C13shouldbe selected theS-T-Cnumberis necessary. Combinin-g is: gageto beemployed 0 E ED-DY-03t CF-350/OPtion -13_ . 2.and run over the sidesof the gear for conleclion attachmeltof to laryer wires.A gagelength which is small with respect to the frllet radiusshouldbe specifiedfor this application. The maximum test temperatureis not a consideration in this case. S-T-CNumber. in contrastto 2.andthetestperformedat constant temperaure. Options -For protectionof the gagegrid in the test envishould be sPecified. and single-grid gages can be employed.A length of 0..Ideally. Becausethe normal choice of grid alloy for static strain measurementat room temperature is the A alloy.The polyimide (E) backing is preferred becauseits low elaitic modulus will minimize reinforcement of the plastic model. a gagelength of 0.S-T-C30. expected 6. 5. GageDesignations: Fromtheabovesteps.2.t In other areasof the model. OPtion L is preferableover Option LE becausethe encapsulationin the latter option would add reinforcement. (because ofstockstatus). Resistorce- In the ED-Seriesversion of the 03lCF gage pattem. DytramicStressAnalysisStudy of a Spur Gearin a llYdraulicPumP areto be madeat theroot of thegear Stnin mensurements pump Thefillet radiusat thetooth is operating.38 mm) is preferable. the directionsof the princiPal axes are not known. E.thegagesshouldbe self-temperato matchthe modelmaterial. the E backing is the most suitable choice. 6. Optrons-Excessive heatapplicationto the testmodel during leadwire attachment could damagethe material.and preYentsthe use ofpreattachedleads.this case. sinceonly dynamicstnin is to be measured. furthermore. B.125in fo rangefrom0" to +180"F(-20' to +80'C).panicularlyreinforced notalwaysfeasible. The higher resistanceshould usually be selectedwheneverthe choice exists. Option ronment.the sfain signals must be tlansmined through slip rings or tfuough a telemetry system to get ftom the rotating componentto the stationary instrumentation.vary widely in thermalexpansioncoefficient. in selectirg the 2508F over the 250BG.031in (O8 rzrz) is selected.the resistancewas determinedirl Step 2 when the higher rcsistancealtemativewas selected from among the gage pattems:i.but this is ture-compensated . Resistance-Ir. -J. The combinadonof the E backing and the D alloy defines the ED sase series. and the 250RD over the 250RA.40 or 50 shouldusually For unreinforced If a mismatchbetweenthemodelmaterialand be selected. a "planaC'rosette should be selected.This requirementnecessitates the small leadwiresafter gagebonding.sincePlastics plastics.since it is well within the recommended temperaturerange for any of the standardbackings.thesftaingagesto be usedare: L (single-grid) EA-30-250BF-35OiOption L (rosette) EA-30-250RD-35O/Option Gage Selection: L GageLength . encaPsulation.In the light of thesecousiderations. and will be advantageousin this instancein improvingthe signal-to-noiseratio when slip rings are used. plastic.and very small leadwireswill be attachedto the gagetabsat 90' to the gdd direction. and a three-elementrosette will be required. Becauseof its high-resistancegrid.015 in (0. the EA Series should be selectedfor this application. For this purpose. S-T-CNunber -D alloy is not subjectto self-temPerature is compensationneededfor these tests nor compensrlion. A gagepattem with both solder tabs at the same end should be selectedso that leadwire connections can be located in the clearance area along the root circle betweenadjacentteeth. Becauseof the limited clearancebetweenthe outsidediameterofone gear andthe root circle ofthe matinggear. Gage Series .[n the EDSeriesdesi-snationthe two-digit S-T-C number is replaced by the IenersDY for "dynamic.1 for A and K alloys). toothwhilethe are (o[ andtesttemperatures 3 nm) about root is 0. theWK gagesarepreferredbecausetheyhaveintegralleadwues.8x 10" per'C).6 nrn) representsthe best compromisein view of the strain gradients.ly specified Gage Selection: .attentionwasgiven to the fact that all threepattemsareavailablein the WK Series. Thisoptionis integralsolderingterminals. Options. but material. howevef.Preliminary design studies using the Photostuess photoelastic coating technique indicate that a gage length of 0. suggestthe selectionof 060WT and' ing requirements 060Vr'Rgage patternsfor the stackedrosettes.Eifter theSK or WK Seriescouldbe selected. the single-grid for on. and space for gage installation. and is therefore to stacked rosettes. with the requirementfor staticas well as dynamicstrain clearlydictatesuseof K alloy for the grid measurement.as in this case. S-T-CNun&er. with the higher 6. not aDDlicable gages. 45-degree rcctangular rosettes are required.C.9 x lO{ per'F (8. Resistance gagesshouldbe specified because of thebenefitsassociat€d gage resistance.with a thermalexpansion ficientof 1.The titaniumalloy usedin the wing tip coefsectionis rhe6A1-4Vtype. GagePattem. S-T-Cnumber05 is theappropriate GageDesignations: W WK-05-062AP-35o/Option wK-05-06owr-3s0 wK-o5-06owR-350 . 1. there are some areasof the wing tiP where single-grid gages and two-element "tee" rosettescan be employed. GageSeties-The maximumoperatingtemP€rature.which is compatible range.with informationaboutthe sEessstateand directions of principal axes gained ftom the photoelastic coating studies.andwill be a dominant factorin the gageselection. Flight-Test StressAnalysis of a Titanium Aircraft Wing Tip SectionWith.areasofpeak strain.the foregorcsettesshouldbe selected. K alloyof choice.350-ohm 5.Option{ with is advantageous. -14- .where principal strain directions vary with the nature of the flight maneuver.For easeof gageinstallation. a Missile Module Attached The operatingtempetaturcrangefor strain measuementsis from -65' to +450'F (-55' to +230"C). Gage Length . The strain gradientsare sufficiently steePthat stacked From Catalog500.and the 062APpatternfor the single-gridgage. and lryithout.062 in (1. with thespecifiedopemtingtemPerature o along 3. 2.In makingthis selection.In other locations.lvhen available. .! ENVIRONMENT 3..Showewru. MATERIALTO BETESTED Description coefficientof Expansion Temperature Silicon CarbideAbrasion ConditionerA 5A Neutralizer AllowableSurfacePr€pa.surhce contouti obsttuclions. GAGEINSTALLATION Indoor0 Humidity T€mperature Approximate Outdoorfl AND CIRCUITS INSTFUMENTATION ExcitalionVoltage Descriotionot FleadoutInstrument Clrcuits: t/4 BridgeD 1/2Bridge0 Fu Bridge0 LeadwireLengths 5. GENERALINFOBMATION Numberof TestSpecimens Numberol tndude st<etchot test pieceshowingdimensions.- VISHAY V StrainGageApplicationRequirements Title Name Phone Company Address Date 1.ation: ppm D'F f|'c YEsO ttoD YesO NoO Yesfl NoO Ch€micalSotuents(specilylimitations) MaximumAllowableBondingPressure MaximumAllowableCurETemDerature .and allowadegagingarca.imate s'ain field. RangeOuringTesl T€mperature TestDurationor NumbErof Cycles 'Iime MarimumTemDerature at MaximumTemperatur€ Descriptionof Tesl Environment 2. lncludaa desc plion of all specialrcquitemenE. it Known. TESTDESCRIPNON Sialic fl MaximumStrain Dynamicf. 2 Reference . by design. and.It is purElydueto temperatuechange.a[d. The electrical resistaDceof the strai! gags varies not only with strain. fr a n ) = tl "E^c +^F(. When the underlying phenomeaa are thoroughly utrderstood. the resistauce strain gage.the gage grid is forced to undergo the same expansion or conEaction._v lo(4a)r'_ a o ) l d r \h)no f- (l) I - VISHAY U I NEASUEEIIHIIS I l@wPl €Copyright Measurements Group. thermal output (soE€times rcferred to as "temperatffe-induced apparcntstain") is clefine4 and the causesof this effect are described.StrainGage Tempetature Effects t- T-t ' StrainGageThermalOutput and GageFactorVariationwith Temperature L0 Introduction u Ideally.tt + _l . accompauiedby numerical examples.a subsequentchangein the temperatureof the gageinstallationwill normallyproducea resistancechangein the gage. Unforfimately. themechanical (stess-induced)strainin thetestobjectto which the strain gageis boncled.the gage /actar.0ThermalOutput to a stain indicaOnceatrilstalled straingageis coEnected tor and the instlumentbalanced. expressedin terms of unit resistancechange. itseu varies with temperature.Becausethe grid is. as a r€sult. the electrical resistivity of the grid conductor is somewhattemperature dependent.0. but with temperatureas well.eaeea$e-siglifiea$t errors if not pmperly accourted for. if not contolle4 can be mucb greater than the magllihrde of the stai! to be measuled. In Section2. o Thermal output is poteutially the most serious eror source in the practice of static sEais measuremetrtwith stain gages. and it is usually necessary to either provide compensationfor thermal ouq)ut or corlect the strain measwementsfor ih presence. andunrelatedto. Methods for the simultaneous correction of both thermal output and gage factor errors an glven in Seaion 4. In addition. is somewhatless tlan perfect.This temperature-induced resistancechangeis independentof. this error source requires carefii consideration. a stsain gage botrded to a test part wodd rcspond or y to the applied strain in the partt aud be unaffectedby other vadables ill thE environment.l. when measuringstrains at temperaturesremote from room temperdture(or ftom the initial balance temperatureof the gage circuit). 2.Typical magnitudes of. To th€ ext€Et thal the thermal expansiou coef[cient of the grid differs ftom that of the substate. . Thermal oltput is causedby two concurent and algebraically additive effects in the strain gageinstallation. . Section 3. With tempemtule change. the errors can be confolled or yirtually elimioated by cpmpensationor correction. or ia any temperahrre range. followed by the commonly used methods for compensatiouand conection. At any temperatue.ord contributiotr to thermal output is dus to the differential thennal expa$ioo between the grid cooductor and the test part or substratenat€rial to which the gageis bonded.the thermal ouq)ut becomes: .Inc. aad. and the net thermal output of the strain gageis the algebraic sum of these. the grid is mechanically strained in confomiqg to the ftee expansion or contraction of the substraie. . Each of the two thermally induced resistancechalges may be either positive or negative in sign with respect !o that of the temperature change.in cornnon s/ittl all other senso$.and is thuscalledtheriermnI ou@utof be gage. The se. shain sensitive. First.In fact.\ 1 .l x.1993 All RighisReserv€d. the substrate expands or contacts.0 of :dnisTech Note.0 Eeats gage factor variations with temperature in a similar but briefer manner since this error source is generally much less significant. however. These deviatious ftom ideal behavior can be important under certain circumstances. since the strain gageis frmly bonded to th€ substlate.the gageexhibits a rcsistancechangeproportional to the differential expansion.Thus. the gageresistancevaries with tempelaturc..the thermal output are then given. the eror due to tbermal output. the relationship between strain and resistancechange. differencescan be expected sinca stluctural materials vary in thernal exPansion characteristics Aom bt to lot. (1) to account for the fact that the stain io the gage gdd due to differential themal exPansionis equal-biaxial.zsK)l is incluiled in Eq.The illustraor correction sbowsdistincflythenecessityfor compensatioa are made fu]an to be measurcmeats static stailt tiou if accurate chatrges. that thermal output depends not only on the nature of the sttain gage.ntaining pe'Jrffiein the testenvirowaent.t | & /za Kr = transversesensitivity of the strah gage. thatis.becausea1lof the coefEcients s'ithin the brackets are themselvesfunctions of teEperature.roomtemPeratue)\ffith tary rcferencetemperature rcspectto which the thermaloutputis measued. (1) by the gagefactor setting of the instrument. the gage faclo! of the 5trail gagc (as specifiedby the packageE[gileelirg Data Sheet)is ideotifredasFa' to distinguishit Aoru the gagefaclo! scttidg of the measuitrg ilstsumetr! derct€d here by Fr. the thermal output of the gage is usually expressedin staitr units. while the gage factor. (2) is superimposedon the gage outputdue to tb this TechNotc.the therEaloutPut from Eq. in consistentunits: fanl | =: | = unit chanse irt resistancefrour the initial referby changeir temenceresislance. be difrEent ftoE that ofthe ga€e.bonded to a specified subsEatematerial. as employed iu Micro-Measuements straia gages. v0 = Poisson'sratio (0. These data are illustrative onln and uot for usein makitrg coGections. underconditionsof ftee thermalexpansion for thesubstrate.and . bonding and encapsulating materials. l.Ro. F6.where.Some of the nore importatrt are: test sPecimenEaterial aud shape. is ihportad. with a principal strain ratio of 1/(-0.MeasulemeDts in its tests. The best practice is always to evaluateooe or more gagesuader thermal conditions as nearly like dlose to be encouutercdin the testing program aspossible. Eyen itr caseswbere applications involve the same matedal as that usedby Mcro. stallatiouis subjectedto a tempemture /7.L 2).1 . in fact. With self-temperaturecompersaaot (Section 2. refers to the stai.however. Bdcarise-oftEiS. the enorsdueto thermaloutputcan becomeextremelylargeastemperatuesdeviateftom the a$i(ordinarily. I = Ia^) l. This distioctio.grid alloy ard lot. Thus. IEMPEBATUFE-'C It should oot be assumedftom the forE of Eq. the strain magnituderegisteredby a stain indicator(with a gagefactor settingof Fr).ad = di. asa Eatter of codvedeDccor utility.285)ofthe standardtestmaterial used ir calibrating the g€e for its gage factor. wheuthe gageinchange. -2- -'F TEMPEFATURE Fig. pleoelyAeeof mechanicallyor thermallyinducedstesses.it shouldbe remarked that if it is feasibleto bring the gagedtestPartto thetesttemthetestpart comm?I. For conveniencein corecting measuredstrah data for ttrermally iaduced resistance chauges. difWhenmeasuringstress-ilducedstrainsat a temperature ferentftom the initial balancetemperalue.encetemPerahue. "aused perature resulting in thermal outpul BG = temperature coefncient of resistaoce of the grid conductor Fc = gage factor of the saain gage.ffetence iu thermal expansion coefEcients of substrateand grid. It sbould be noted. The equation clearly demonstrates. sincetbegagefactor senilg of theilstrulne Eay solretiE s. respectively Af = temperature change &om an arbitrary idtial rcfef. gageseriesatrd PatterE.meimdl output data arc meanilgful only when refened to a particular t ?e of saain gage. The conection factor for transverse sensitivity t(l + Kl)/ (1 . environmentirvolving temperature With respectto the latter statement. Figue 1 shows the variatioq of thernal output with tomperature for a variety of strain gage alloys bonded to steel.&'i"'" €. but also on the material to which the gage is bouded. It is trever possible for MicroMeasureBeutsto prcdict exactly what the thermal outPut of any gage will be when the uset has bonded it to a test structure. that the curves for cotrstartan aud Karma are for qon-self-temperatwe-comPensatedalloys. (1) that the th€rmal output is linear with teEperature change.s seositivity as calibrated in unia:ial stress state.To = -= l- F rJ (2) fl wberc:ey6 = thermaioutputin stain units. mechanical strain.285). dividing Eq. causilg the measurementto be in error by ttlat anounl Many factors affect ths lhermai outPut of stsai! gages. and instailation procedures.traNvslse seositivity of th" gage. (as.Thermatoutputvariation with temperuture lor severul strain gage allols (in the as-rolleilmetullurgicalcoruIi' tion) boniledto steeL As inrlicatedby Fig. the thermal ouQut chalacterisiics of these alloys are adjusted to minimize the errot over the normal ralge ofworking iemPerahres. point-by-point correction for thermal output will usually be trecessary. it is rare that the foregohg requireEents can be satisfie4 aqd tbe stressaoalyst ordinarily fitrds it necessaryto take full account of thermal output effects.siuce identical resistaacecha. There is.atrd the two signals are readily separable. The two gages in adjacent arms of the Wheatstonebridge circuit then fttnction as an activehalfbridge. columns.od. whetr no temperaturechange occumbetweenthe stsess-fteeand stessed conditions.balarce the sEaitr indicator for zero stain under these conditions. .Examplesillustrating lhe useoJa secorul(compenbridgearm to sating)strain gagein an adjacentYFheatstone cdncelthe effectof thermaloutl. the error due to thermal output can be completely elim. however. There is a furlher difEculty in ensuring that the temperatureof the compeusathg gage on the unstrained specimenis always identical to the teEperahre of the active gage.are precisely identical. I-ncluded in this class are ba$ in pule tolsion. it must be recognized that no two stain gages .If. however. diaphngms. G) ACTIVE GAGE AL2 L3 cLl (b) P G) Fig. the thermal outputs of the two gagesshould be identical. Iu general. when the tbree identity criteria already mentioned can be well satisfied. In these instarces. For exanple. staio measulementscan be made without compensatiag or correcting for thermal outPut. when stain measurementsare to be made otr a beam which is thin enoughso that under test conditiotrs the tempemtules on the two oPposite surfacesnormal to the platre of bending are the same. no thermal output error exists whsn subsequentstraiE measursments are made at this tetnperature.even Aom the same lot or package. in the case of purely dynaEic strain measurcments. it is sometimes very difEcult to arrange for the placement of an utrstrained specimeuof the tEstmaterial in drc test euviroDment and even more difEcult to make certain that the specimenremains unsEainedunder all test conditioas. . thermal output may be of tro consequence.ut.with non-self-temperature-compe$ated gages.a specialclass of skain measurement applications which is particularly adaptable to compensationof thermal ouq)ut with a secoudgage. 2a). but connected itr atr adjacent arm of the Wheatstone bridge circuit. This problem becomes poticularly severe whenever tiere are temperature gradients or tmnsientsin the test environmetrt.This is because the frequency of the dynamic stain signal is usually very high with respect to the ftequetrcy of temperah.This class coosistsof those applications ill which the ratio of the strains at twb different but closely adjacetrt (or at least thermaly adjaceot) points on the test object are known a priori. al1stessed within theirrespective proportional liEits.leaving only the stress-inducedstrain in the active strain gage to be rcgistered by the stain bdicator. the sameconsiderationsapply to the leadwires. where there is no need to maintain a stable zero. the method of compensatiagwith a dumroy gage is a very effective tecbnique for contolling the thermal output error. For most static strain measurementtask itr the general neigbborhood of room temperatue. A.thereis combined static/dynamic strain. etc. Under thesehypotbeticql conditions.An4 asindicated in the precedingparagraph. Fimlly. In practice.1.gagedifferencesin thermal outputmay be so -3- great as to preclude duumy compensation fo! temPeratures which are remote ftom room temperature.1 Compensation for Thermal Output 2. 2.the gags-to. the compensatinggagecan often be located sEat€gically oo the test member itseif so as to provide two active gageswhich undergo the sametempeEture variations wlile sensingstraiDsthat are prcfsrably opposite i! sign aqd of known ratio.mouDted on an unsfiained specimenmade ftom the identical material astbe testpad. moreover. In theseapplications.ngesitr adjacent alms of ths Wheatstonebridge do not unbalaacethe circuil the thermal outputs of tbe active and dumrny strain gages should cancel exacdy .or if the ftequency of iemperaturechaugeis of the sa. For this to be pr€cisely true rcquires additionally that the leadwires to the active and dummy gagesbe of the same length and be routed together so that the temperature-induced resistance chaogesalso match identically. thermal output effects must again be considered. and subjectedalways to the same tempelahrre as the active gage. To begin with. the two straio gagos can be installed directly opposite each other on these surfaces (Fig. The principal problems etrcoutrteredin this method of temperature compensationare those of estabiishing and maintaining the tbrce sets of idsntical conditions poshiated above. an identical compensatiog or "duEmy" gage .. aod the static component must also be measured. but the difference rnay become evident (atrd significart) when measuring stains at temperahue extemes such as those involved in high-temperatule or cryogenic work.1 Compensating @ummy) Gage lnL WE In theory at least.itratedby employing.2 .shain rcference. beams iu bending.rif-- '- Also. ia conjunction with the "active" suain gage. the difference in therrnal output betweer two gages of the sa-@e type ftom the samelot is negligible. The active haif bridge thus formed will give efiective temperahue compensation over a reasonable range of temperatures and.In other words.[e chatrge.meorder as the stain frequency. Such ftansducers. Figure 4 illustrates the thermal output characteristics of typical A. completing the bddge circuit witb a 'bridgestable fixed rcsistor ir the adjacentarm (Fig. respectively). Fig. If correction for thermal output is needed. will double the outPut sigtral from the Wl.A single self-temperature-compensstedstrdin gage in a three-wie quarter-bri. j .are suchthat thesealloys can be processedto mininize the thermal output over a wide temperaturerange wben botrded to test natedals with themal expansioncoefriients for which they are htended. The designations of Miclo-Measulements self-temperaturecompensated strain gages include a two-digit S-T-C uumber ideutifying the qominal thermal expansion coefficient (in ppm/"F) of the material on which the gage will exhibit optimum thermal output characteristics as shown in Fig. the gagesare designed to mininize the thermal output over the temPerah. with both gagesmaintained at the same temperature.2 Self-Temperature-Compensated Shain Gages o lI The metallurgical propsrtios of certain stain gagealloys in particular.30. In a beam.tsat or near room tempenture to usea single selfteEp€raturc-compensatedgagein a quarter-bridgeaEangement (with a tbrce-wle hookup).ce for stress analysis meaaurernents.eatstonebridge.And the samemethod of compensatiouis universally employed in commercial strain gage tlansducers. however. for that matter. . aud the bar in torsion must riot be subject to indeterEirate axial or bending loads.ncesare such that a pair of matched gages can be used LI adjacentarEs of the bridge circsit. for example.06. 2c). Stsaingages employing these specially processedalloys are referred to as seIf -temperai4re-conp ensated. 4.the requirementfor a matcbi€ utrstraineddummy gage in the adjacent arm of the Wleatstorc bridge has been relaxed considerably.uerarge from about 0" to +400'F (-20" to +205"C).That is. The percenterror in strai. oldioarily employ fttll-bridge circuits and special a[angemeats of the straiD gagesto eliminate tle effects of exEaneousforces or moments. S-T-C numben of 30 aud bigher are iffended primarily for o i 'J . constantanand modified Karma (Micro-Meastuements A and K alloys.it can be made as shown in the followins sections. accompaniedby an augmentedoutput signal lby the factor (1 + y) in this casel.rallyplaces. 1+100 5-o I e *ao : -4oo i -ro -€oo + -100 2.strain Since the advent of the self-temperature-compensated gage. that the accuracy of the strain measurementis somewhat dependeEt upotr the accuracy v. gages.strain hdicato$. 4 . It is now normal practice when making strain measureme!.03.13. when circumed in Sectian describ in the manner sta.09. excellent tempemtur€competrsationcar be achievedover a wide temperatlrrc range.When the self-temperature-compensatedstrain gage is bonded to material having the thernal expansion coefEcient for which the gage is intended.umeasurementis approximately equal to t'(1 + t/) times the percent euor in Poisson's ratio. The resuit. again. is compensationof the tlprmal output. there must be so indeterminate axial or torsional loading.As demonstratedby the frgure.strain measurementscan often be made without the necessity of conecting for thermal output. As in the caseof the bean.and K-al1oy self-temperatue-competrsated strai! -4- +100 PENAfl'RE-'F )300 +400 Fig.ald 50.40. excellent tomperahre compensation cau be achieved.18. for a bar in Pure to$ion (Fig' 2b)' the two gagescan be installed adjacentto eachother and aligned along the principal axes of the bar (at 45" to tbe lorgitudinal axis). Such ' completiou resistors. Similarly. MicroMeasurcme s constantatralloy gages are available in tle fo1lowing S-T-Cnumbers:00.are supplied by Micro-Measuremeutsatrdare incorpoEted i. however. It should be borne in mind in this application. with very low tenperatue coefEcieutsof resistance.he relationship hetween the strains 4t the two locations must be known with cenainty. straitr gagescan also.dge circuit exemplifies modern strain gage pradi.1'1.1. This requirement for a priori knowledge of the sbain distributioo ach./ith which the Poisson'sratio of the test material is knowu.fferent than when the gageis mounted on a flat surfaceof the samematerial.nmost Eodem.si[ce the saains sensedby the gagesarc equal in magnitude and opposite itr sign.Typical thermal ouE ut variation vith tenperatute for self-temperature-contpensated constantan (A-alloy) and modifud Kann (Ka oy) strain gages.along with a doubled output signal' When making strain measurementsalong ttre axis of a column or tension link. 15. and when opemted within the temperaturc range of effective compensation. In all strain-measuremeut aPPlicatioqs which involve mounting the compensaring gage ou the test object ilielf. A further caution is necessary when stair gages ale moutrted bansve6ely on small-fiameter rods (or.05.and with one of the gagesunshained (or strahed at a determinate ratio to the othet gage).these and most simila! applications in the class of transducers. the compensatinggage can be mounted on the test member adjacent to the sxial gage atrd aligned tratrsve$ely to the longitudinal axis to sensethe Poisson strain @ig. 3). in small-radius fillets or hol€s)' Hines has shown (seeAppehdix) that under these conditioDsthe thermal output characteristics of a strain gage arc di.be used Self-temperature-compensated 2. TABLE I - Noninal Thermal ExpansiotrCoefficients of EngineeringMaterials a n-uutuln,"o I I ALUM|NUMAlloy, I I I zoz+tt',zozs-ta I ou." I I eenv'-.,uN, coPPER, I I I I I I I I I I I I I I I I I I I BERYLLTUM I cu7s,Be25 | cart.ldge, I BBASS, cu70,zn30 | ERoNzE, Phosphor, I cue0,sn10 | cAsrlRoN, slay I pure coPPER, I cLAss, I Soda,Um6,Silica I o I I I, I I I I Az.31B pure MoLYBDENUM', I I 6.4 11.1 '10.2 6.0 I I I I I I sTEELAlloy, I 4340 | | cerbon, I STEEL, I 1018' 1008, | I I STEEI,Stalnles€, I I AgeHardenable I | 07-1PH) | I srEEL,srainte€s, I lAgeHardenable I (17.7PH) | I STEEIStainless, I I lAgeHardenalle I (PH15-7Mo) | | Stalnless, I I STEEL, (304') Austgnltlc I I STEEI.Stalnle6s, I (310) Austenitic | STEEI-Stalnless, I (316) Austenitc | STEEL,Stainless, I Fenttlc(410) I TlN,pur€ | TlTANlUM,purB I mAi'llUMAlloy, I 8A1-4v' I 1ITANIUM SIUCAIE', I polycrystalline I pure TUNGSTEN, I pur€ ARCONIUM, I type I;:=l 13' 09 If a strain gagewith a panicular S-T-C number is installed on a material with a nooEatching coefrcient of expamion, the thernal output characleristicswill be altered ftom those shown in Fig. 4 by a geaeralrotation of the curve aboBtthe room-temperahue reference point (see Sectioz 2.2.5). When tlp S-T-C lumber is lower than the material expansion coefficient, the rotation is counterclockwise; and when higher, clockwise. Rotation of the thermal output curve by intetrtiodally mismatching the S-T-C number and expansioncoefEcient can be used to bias the therrnal ouEut cbaracteristicsso as to favor a particular working tempemtur€range. l;l |";"I 09 7-O | | 0.8 14.5 2.7 I Ni4ualloy I I NTCKEL-A, Cij:Zi:Nlalloy I ouABrz,tus€d 12.9 I rNcoNEL. Ni-crFoalloy tNcoNslx, Ni{rFe alloy TNVAR, Fg-Nialloy Alloy', MAGNESIUM I riror|El, 3.0 use on plastics. In K alloy, the range of S-T-C numbersis more limite4 and consistsof 00, 03, 05, 06, 09, 13, and 15. For referenceconvenience,Table 1 lists a aumber of engiaeerbg materials, and gives nominal values of the Fabrenheit and Celsius exparsion coefficients for each, along with tbe S-T-C number which would nosmlly be select€dfor strain measurementson ttnt material. The table also ident'des those test materials used in determining the pubtshed thermal output curves for MicrosEain g€es. Measurementsself-temperature-compeDsated 6.6 0.3 1'.6 12.1 I 2.2 Correctionfor ThermalOutput | uponthetesttemperaturc andthedegree of accuDepending l,o I racy requiredin the shainmeasuementit will sometimesbe necessary to makecorrectionsfor thermaloutput,evetrthough gagesare used.In any case, seu-temperature-compensated whenmakitrgstrain measurements at a temperatuedifferent from theinstrumeotbalatrc€leEperature,thei.ndicat€d strainis equalto the sum of tbe stess-inducedstrainin the testobject andthethermaloutputof thegage(plusthesaai! equivalentof aayotherresistance changesin thegagecircuit).With the thermaloutputexpressed in stain units,asin Eq. (2), cofiectionfor this effect is madeby sinply subuacting(algebraically,with sign)thethermaloutputftom thei[dicatEdsEain. l;l | ,":, I 15'. 03' 06 00 I e: I 6.0 5.7 As anaid to theuseri! coEectingfor temp€ratue-dependent properties,the EngineeringData Sheetin eachpackageof Micro-Measurements A- and K-alloy saain gagesincludesa graphshowingthethermaloutputandgage-factor variationwith temperature.Figure 5 is typical (for A alloy) of the graphs suppliedwith the gages.Io additionto plots of thermaloutput andgagefactor variation,polynomialequationsareprovided (in both Fabrenheitand Celsiusuaits)for the thtrmal output cuwe.AJsogivenon thegrapharetwo otherimportantitemsof l',"l | ,0., I tl 5.O 9.6 8.0 1,, I | "' I II t 144 IIiERMAL OUTPUT F- 1 l;l Iil EP i.E Eri Yi :: :! 05 'i3.0 4.4 4.9 0.0 2.4 9g EI 05 *{ iir €? frE ta FE 05' 00. 03 03 rEerEooN:!q!!3!g!!!9[ ou(Purcurycs suppli€dwith Micro-MeasuemenB strai! gagcs. **NomiEal values at ot oear roolr tempelature for teoperatule coeffciedt of expaDsio!values. -5- rEs.PATrqN:!499 cooel!]lzl_ ENcigg Fig,5 - ReplicaoI gqth incluled on the EngineeringData eaahpackageof Micro-Meosuements Sheeta.ccompanying self-tezqterature-compensatedstrain gages. information: (1) the lot number of the stain gages,and (2) the test material used in measuring the therrral output characteristics. It should be noted that the thermal output data are speci6cally applicable to only gages of the designated lot number, applied to the sametest material. 2.2,1SimpleProcedure , = eno €no2.0 E wh*e: Approiimate correction for thermal output can be accomplished most directly and easily using the graph (Fig. 5) supplied in each package of self-temperatue-compensatedgages. This simple method of correction is based on the fact that the gage factors of A- and K-alloy gagesare close to 2.0, which is the standardizedgage-factorsettirg employed ia calibrating the gagesfor thennal ourput. Adjustment of the thernal output data for a different instrumeot gage-factor setting is described in Section 2.2.2. The fust step in the correction procedure is to refer to the graph and read the thermal output correspondi.agto the test tempemture. Then, assuming that the stain indicator was balanced for zelo straitr at room tempemhre (the reference tempemture with rcspect to which.,the thermal output data ei/eremeasued), subtract the thermal output giyetr on the graph ftom the strain measurementsat th€ test tempemture,carrying all signs. This procedue can be expressedanalytically as follows: e=e-ero output corection can thus be made by adjusting tbe data from Fig. 5 (taken at Fr = 2.0) to the culrent gagefactor setting s;659 instrument. This is done as follows: (3) where:6 = urcorectedstrainmeasurcmett, asregistered by the strain indicator. = partially correctod strai! indication - that is, corf rected for the[Eal output, but not for gage factor variation with temperature (see Section 3.0 ar:d. 4.0). er/o = &e$E?J.output, in strain units, from the package Eogineeriag Data Sheet. As an exarnple,assune that with the test part uuder no load and at rcom tomperature,the sfain itdicato( was balasced for zero stain. At the test temperatue of +250"F (+121'C), the hdicated staiu is +2300&€. Refedng to Fig. 5, assumingthat the graph was the one in the gagepackage,the thermal output at test temperah.ueis -100&€. From Eq. (3), the correctedstraj! is thus 2300 - (-100) = 2410pe. Had the iDdicated strain beer negative, the corected stain would be: -2300 - (-100) = -2200pe.1f the instrument were balanced for zero stain at some tempelature other than +75'F (+24"C), the yaltJeof er/o for use in Eq. (3) is the net cbangein thennal output i! going from the balance temperature to the test temperature.That is, e716= e716(72)- e71s(4), canying the sign of the thermal output in eachcase. (4) e'rto = therrtral outPut adjusted for instrument gage factor setting. = €to thermal output ftom gagePackagedata sheet ( Ft = 2 ' 0 ) ' Fl = itrstrument gage factor setting during stlain measuremeut. Continuing the uumerical example, and assuming that the data sheetgives a room-temperaturegagefactor of 2. I 0 for the gage,and that the instlutrent is set at this samegagefactor, the adjustedthermal output is calculated from Eq. (4): tn e'no = -tgg 7 :-! = -95 tr16 And the coEected strain measurementsbecome: 2300 - (-9s) = 2395pe and, -2300 - (-95) = -22Q5p.e As shown in Fig. 5, the gage factor of the strain gage varies slightly with tempeEture. ffien this effect is significant relative to the required accuracy in s[ain measulemenqthe gage factor of the stlain gagecan be co[ected to its tesFtemperah.Ee value (S€cfrbz 3,I), and the gage factor of the hstument set accordingly. The resulting ilstrumeat gage factor is substituted into Eq. (4) to obtaid the adjustedthentral output, which is then subhacted algebraically from the iadicated shain to yield the stress-inducedstain. o 2,2.3 Extensive Data Acquisition If desired, for exiensive sEaiD measuremeatprograms, the thermai output curve in Fig. 5 can be replotled with the gage factor adjustment - either room-temperatur€or test-temperature - already incorporated.Upon completion, the thermal output read from the rcplotted curve can be used direcdy to correct the indicated strain. This procedure may be fouud worth the effort if many stain readitrgsare to be taken with one gage or a group of gagesfrom the samelot. For conyeniencein computerized correction for thermal output, Miqo-Measuements supplies, for each 1ot of A-alloy and K-al1oy gages, a regression-fitted (least-squares)polynomial equationrepreseuting the thermal outpul curve for that lot. The polynomial is of the following form: er/o -- Ao + ArT + Azf + erf +Ant' (5) 2,2.2 Adjusting Thermal Output {or Gage Factor It should be trotedthat the instrumentgage facto! sefting employed in recording thermal output data is standardized at 2.0 for all Mcro-Measurements A- and K-alloy gages.If, during stain measurement,the user's ilstruEetrt is set at a gage factor differcnt from 2.0, the themal output componentof the indicated strain will differ accordingly from that #ven itr Fig.5. This difference is usually no more than severalpercent when the instrument gagefactor is setto tbat of atrA- or K-alloy gage. A modest improvement in the accwacy of the thsmal -6- where: f= tempenture. Ifnot itrctudeddirccdyon thegraph,asshownin Fig. 5, the A, for Eq.(5) caobe obtainedftom Miqo-Measuecoefacients mentson requestby specifyingthelot uumber. It shouldbe bomein mind that the r€gessior-fittedequations,like thedataftom whichtheyarederive4arebasedon an hstrumentgagefactor of 2.0; and,for greatestaccuacy,the therna.loutput valuescalculated&om the equationsmust be I I :l ,dH a | , 2.2.5 S-T-C Mismatch adjusted to the gagefactor setting of the instrumetrt if other thao 2.0. As an altemative, the Aj coefEcientsin Eq. (5) can be multiplied by the ratio 2.0/Fr, where F, is the instumetrt gage factor used for strain measuremeal Another cotrsidelation which should trot be overlookedis that tbe supplied themal outPut data and equations are applicable only to the specified lot of gages,bondedto tbe identicalmaterialusedby Micro-Measuremetrts in performi-Bgthe therrnal output tests. When a strain gageis employed on a material other than that usedin obtaining the matrufacturer'sth€rma1ouq)utdatafor that lot of gages,atr S-I-C mismatch occurs.In such cases,the tbermal ouFut of the gag€will differ from the curve supplied ia the gagepackage.Consider,for example,strain measurem€otsmade at au eleyated tempemtureon Monel with a stain gage of 06 S-T-Cnumber,calibratedfor thermal output on 1018steel(Table 1). The thermal expansion chalacteristics of Morcl are somewhat different from 1018 steel, and the strain gagewill produce a correspotrdirgly differeqt thermal outPut. Thus, if accurate strain measuemert is required, the thermal output chancteristics of the gagebondedto MoDel must be measued over the test temperatue raqge as describedin Sectlbz 2.2.4. For small temperaturcexcursionsfrom room tempemture,the effect of the differencein expansionpropertiesbetweenMonel aad 1018steel is trot very significant, and would commonly be ignored. 2.2,4 Accuracy anal Practicality First-Eatrd Measurement of Thermal Output There is a limit as to just how far it is practical to go in adjusting the mauufacturer's thermal output data in an attemPt to obtain greater accuracy.In the fust place, the therEal outPut curve provided on the Engineering Data Sheet (or by the PolyIlomial equatioo) represents an avemge, since there is some variation in therrnal output chajactedstics from gage to gage within a lot. Alrd the width of the scatterbandinffeases as the test temperature departs further and further from the roomtemperaturereference. The spreadingof lhe scatterbandis approxirnately linear with deviatior from room temperature,at least oyer the tempeiatue range fron +32" to +350'F (0" to +/ 75'C) for which scatter data are available. At be 2c (95Eo) confidence level, the variabfity for A alloy cau be expressedas !0.15 LL!"F ( x0.27ll6f C), a.odtlat of K alloy as!0.25pd'F G0.45tt €fC). Thus,atatest temperatuleof +275"F(+135"C), th" 2a width of the scatterbandis $30p€ for A alloy, and a50p€ for K alloy. . ' , ':'-. ;. i ti+ lt l_ fi *... On the other hand, when the difference in thermal expansion properties between the thermal output caiibration material and the Eaterial to which the gage is bonded for stressanalysis is great, the published therrnl ouEut curve cannotbe used dircctly for making corlectioos. Examples of this occur in coastaotao straiq gages with S-T-C uumbers of30, 40, and 50. The princi pal application of these gages would normally be strain measureEer on high-expansion-coefEcientplastics- But the thermal (and other) properties of plastics vary signifcantly from lot to lot and, becauseof formulation differences, eveumorc seriously from maaufacturer to manufacturer of uoninally the sa.meplastic. This fact, along with the general instability of plastics goperties with time, temperature,humidity, etc., createsa situation in which there are no suitable plastic materials for use in direcdy measuring the thermal output chamcteristics of gageswith S-T-C numbers of 30 and above. As ao admitledly less-than-satisfactoryaltemative, the thermal outputdata provided with these gagesare measuredon 1018 steel specimeff becauseof the stability atrd repeatability of this material. fortn"t oore, the thermal output data given in the gagepackage *ere necessarilyneasured on a particular lot of a particular test material (seeTable 1). Difierent materials with the same or closely sim.ilarromiaal expansioncoefficients, atrdevetrdifferent lots and forms of the samematerial, may have significantly different thermal expansion characteristics. From the above consideratioos,it should be evident that in order to achievethe most accwate corection for thermal output it is generally necessaryto obtaio the thermal output data with ttle actual test gageinstalled otr the actual test part. For this purpose, a thermocouple or resistance temperature sensor is installed immediately adjacent to the straitr gage.The gage is then connectedto the stai-u itrdicator and, with no loads applied to the test part, the inshument is balanced for zero strain. Subsequendy,the test part is subjectedto the test temperaffeG), again with no loads applied, aud the temperature and irdicated straitr are recorded under equilibrium cor&tior.s. lf, throughout this prccess,the part is completely free of mechadcal atd thermal stresses,the resulting strain indicatiou at any temperature is the thermal output at that temperahre. If the ilstrument gage factor settiag during subsequentsEain measuremetrtis the sameas that usedfor thermal output calibration, the observedthermal output at any test temperahuecatrbe subtracted algebraically ftom tle indicated straitr to aiTive at the coEected stain. Otherwise, tile therrnal output data should be adjusted for the differcnce in gage factor settings, as described ia Sectinn 2.2,2, pior to subtsaction. As a result of the foregoing, it is always preferabl€ when rneasuringstrains on plastics or other materials with 30,40 or 50 S-T-C gages (at temperaturesdifferent ftom the imtrument balanceteBperature) to first Experimentally determinethe thermal output of the gage on the test matedal as described in Section 2,2.4. Using these dat4 coEectioDs are then made as usual by subtracting algebraically the thermal output from the measuredstrain. For use as a quick first approximation, the thermal outPut characteristicsof 30, 40, or 50 S-aC gages on a plastic (or on any other Eaterial) of knowu coefrcient of exPa$ion can be estimated by reversing the clockwise rotation of the thennal output cuwe which occurred when measudng the chamcteristics on a steel specimen.Assume, for example, that a 30 S-T-C gage is to be used for strain Eeasuemetrts on a plastic with a Joistaot expansion coefEcient of 35 x 10'6/"F (bl x rc6rc) over the test temperatue range. Assume also that the expansion coeficiert of 1018 steel is constantat 6.7 K lo'ol'F (12.1 x lNfC1 over the sametempemtulo rarge. With tbe saain indicator set at the gagefactor oftbe strain gage, so that F/=Fc, and noting that the ratio (l + Kt)/(l - /04) is trormally close to unity for A-altoy gages,Eq. (2) catr be rewritteB h simPufi€d (and approximate) form as follows: In order to corect for thermal ouq)ut i.u the manner described here, it is necessary,of cowse, to measurethe temperature at the stain gage hstallation each time a strai! measurcmetrt is made. The principal disadvantageof this procedure is that two channels of instrum€Dtation are preempted for each stmiu gage - one for the strain gage proper, and one for the thermocouple or resistancetempemturesensor, -7 e n n = l P - a n-l)A T + a s A T "" l.% - (6) As shown in Fig. A. Although generally applicable. at best.when j ustified by accumcyrequircments.tfunction [from (A) to (B)l when a strain gage is installed on a material of higher thermal expansioncoefficientihan that usedb! the nanufacturer in S-T-C caWration. steepensnoticeably outside of this range. The procedue just demoustratedis quite general. fot atemperaturerange of. while very modest and flat between room temperatwe afi +200'F (+95'C).ed Karma (K al1oy) is distinctly different from that of the A and D alloys. the procedure is also limited itr accwacy becausethe expaasion coefflciene i! Eq.+-""ldr. The variation of gagefactor in the D alloy.Rotation of the themal outP. Eq. \ fc ) sotvingEq.oo I dr * a. (8) statesthat the thermal outPutcurve for the 30 S-T-C gagemountedon 1018steelcan be convertedto that for the samegageroountedotr a 35 x lO-6/'Fplasticby additrg to the original curve the prcduct of the difference in exPansioo coefficients aod the temperaturedeYiationfrom room temperaBulre(always carrying the proper signfor the tetnperaturedeviarioz). correctioDEay not be Practical.on4. direct measurement. the gage factor variatioa with temperatur€ for modifi. 6 .dePonding upon the alloy involved. ntrt=l+-dclAT+354? (7b) and.0 GageFactor Variation with Temperature The alloys used in resistancestain gagestypically exhibit a changeitr gagefactor with temperature.the error due to this effect is small and can be ignored. the thermal output data supplied in the gagepackagecatrBotbe aPPliedmeaningfuliy.aod can be used to predict the approximate effect of any mismatchbetween the expansioncoefrcient used for obtaining the themal outPut curve on tle gagepackage data she€tand the expansioncoeffrcieot of some other material on which the gageis to be installed..' -re. (7b). It should be bome in mind that the foregoing procedure gives.(Note: Although the remaitrder of this example is carried through in only the Fahrenheit system to aYoid overcomplicating t}Ie trotation.f. TOMAIEFIAL FFOM$T.Irl some cases. This is becauseD alloy is used prirnarily for purely dynamic strain measurement'undor which conditions otber enors in the Eeasulement system may greatly overshadowthe gagefactor effect.corection for the gagefactor variation may be necessary. the test temperature. Tbe gage factor Yariatiotris nearly . as described in' Section 2.2'4.) ffien specifically applied to 6.and the required accuracyin straiu r[easurement. (6) becomes: (a \ lic ) enn P .7 and 35 x l0-6/'F materials. qay. into andsubstitutins ) (8) €noes)= €no6. correction may not be Becessary. a rough approximation to the actual thermal output when therc is a mismatch betweeo the exPansioflcoefEcietrt of the test material and the selectedS-T-C number of the straitr gage.57 x 104/rR ASMEISUFED. In others.S--f4 3{ FO|! AONOED . typically being in the order of 1% or less per I00"F (2V" or lessper 100"C). However.At morc extremetemperatures. Eq. even for temperatwes wherc the gage factor deviation is several pe!cent. 7 that the effect in the A alloy is essentially linear.0 .T*(35-6'7)AT In words.S-T-C gage as originally measured on a 1018 steel sPecimetr. 7 . |. 3. about room tempemtue.tar ' ' . aud quite small at any temperatule. -8- It cau be seeu from Fig.Gagefactor variation with tempersturefor constan' tan (A-allo!) and isoelastic (D-alloy) strain gages' FE -'1oo o +300 +1oo +2oo TEMPEMTUAE-'F +4oo +500 TOlol SSIEEL(d .C 30FO1IBONOED RESFONSE EXPECIED B-APPROXIMATE wlIHc-35r1g4]'E Fig.u=l ' Qa) ( n^ l €-r-.--. T\trs. the correction can be made as shown in Seclloz 3. (6) arc themselves functions of tempelature for most materials.the temPeratue of the strain gageis sigtrficantly bigher than that of the test Part.O") f". the same procedure Produces the equivalent result in the Celsius system.U. Figure 6 shows the thermal outPut curve for a 30. Whetr accuate correction for thermal output is requted. or combined with the thermal outPut correctiotr as in Secti. rG \ Eq. A further limitation in accuracycatr occur whenmeasuringstrainson plastics or other materials with poor heat transfer characteristics. -'C TEMPENATURE 5d TEMPEAATUI 3E Fig.t100"F ft50'C). 8.and as rotated counterclockwise to aPproximatethe-r€sponseotr a plaso/"F tic with an expansioncoefEcient of 35 x 10 due to selJ-heating. is fughly recommended. (9).'Refedry ro Fig. using Eqs.was registered with tbe gage factor setting of ftre strai! indicato( at Fl.K-ailoy girgeis 2. 8 . (9) aod (10). The forms these relatiotrships can take depend upon the measuring circumstances.(10).fromEq.' lr.05(1-0.aF(%)\ | ^\ 1 0 0/ lr! (10) wherc: AF(%) = percentvadationin gagefactorwith temperatureas shownin Figs. the procedure developedhere requircs that the gagefactor of the instrument be set at F1 = .pdmarily upon the strain indicator gage factor setting and the temperatureat which the instrumetrt was balaqcedfor zero strain. 3. This information is all that is required to make the correction. 7 ard 8. it will be fouad that selecthg the first altemative generally leads to the simplest fomr of correction expression. the gage factor at which the thermal output data were recorded.0 (at whicb thetlermal output wasmeasured)to the test temperaftxegagefactor. but one of the following tbree is most likely:t 1. 4F(7a)for thiscaseis -3.thefollowiug sectiongivesequationsfor performingbothcorrectiotrssimultaneously.becomingsteeper with highernumbers.buttheslopeis negthear rvith temperature. = 1875pe ez ' = L82ox.1 Correcting Straitr Measurementsfor GageFactor Variation with Temperature The standardprocedurefor measuringthe gagefactor of a lot of aly particulartype of stain gageis performedat room temperatue.Thus. andno conectionis necessary.05an4 with dreinstrumentsetat this value.however.any strai! measulemeatdata can be coEected (or adjusted) ftom one gage factor to another with a very simple relationship.Also given oD each data she€t is the applicable $aph of gagefactor variatior with temperature. at any temperatureother than room temperaturethe gagefactor is differeEt. (Note: The sigu of the vadation must alwaysbe included. Assume.the gagefactorcontrolof the staio indicatorcanbe setat F2.0 Simultaneous Correction of Thermal Output and GageFactorErrors Relationships are giveu in this section for correcting indicated strainsfor thermal output and gagefactor variation with tempemture.Of course.99 s ubstitutirghto Eq. Fig. and. and a correction may be needed. assume that the room-tenperatuegagefactor of a 13 S-T-C.siDcethis Inay intloducea zero 6hift. e1. Test temperatue 3. 8. but.tbatif thermaloutputcoEectiomaleto be made from the graph(or polynomial equation)on tle Engineerilg DataSheetin thegagepackage.which is given on the EngineeringDataSheetin each of Micro-Measurementsstain gages.0). = -(.) As a numericalexaople. The stmin indicator gagefactor can be set at any value within its control range. €2. for instance. adveandis a fuuctionof fte S-T-Ctrumber. .audF2 the gagefactor at the test tempeature. Room temperature 2.whetrthe test is ktrownwith reasonable temperature accuracyin advance. Gage factor.thethermaloutputdatamustbe adjustedftom a gagefactor of 2.suchasthose in Figs. being usedfor strainmeasuremenl Thefollowingrelationshipis used!o determinethegagefactor at the testtemperaturefrom the tabularandgaphical data suppliedin thegagepackage: -9- 4.F2. Fz= 2.. 2.andbecauseconfusion may ariseia making the correctionsindividually and thencombiningthem. Similarly. 7 and 8. initially. Room-temperaturegagefactor as givel on tbe gagepackage EagiBeErirg Data Sheet3.alongwith its tolerance. Gage factor of gage at test temperatureor at any a$itary temperahre other than room or test temperatue.| l+. No single gage factor is uniquely correct for this situation. and it is desircd to coEect the data to a gage factor of Fz. the straia itrdicator can be balancedfor zero strain at any one of severalstain gage temperatures: 1.4^ r. F*.It is this valueof tbegagefacto!. The corrected stain.is calculated from: Ez= €t 1 JJt2 (e) Whencorrectiugfor gagefactorvariationwith temperature.0.Variationof K-alloy gagefactor with tenperatare andS-TC numben asit is for A alloy. that a strain. gagefacF'i canbet8keoasthepackage-data room-temperatule tor at which the straitrindicatormay havebeenset. Itr gederal.F* = 2. used by Micro-Measurements ir determining frermal outputdata(F = 2. Arbihary temperatue other than room or test temperature fThe irlstsudeot gagefactor setting should lot bc chadgeddurilu a test (afte! zorq balance). of the foregoing.03)= 1.Becauseof this. according to the circumstances.99 atrectsboth the Siacegale factorvariationwith temperature thermaloutputandthestess-inducedstrain. It shouldbe notedil this case.the strain indicationat +450'F (+230"c) is i82op€. assumethat the stair indicator is balanced with the gage at room temperature. (11) to eachcondition: rr. . = l_e . and witlt the gage factor cotrEol set at F*. Because the strain measurementwas made at a gagefactor setting ofF*. opentiag fust at speedly'l. "l L_ . .08 where: Q = indicated staitr.The indicated stai-E a is generally in error due both to thermal output aBdto variation of the gagefactor with temperature .withF* = 2. Asume also that a strain Q is subsequendyirdicated at a temperatureIt qhich is diferent ftom room temperature. As ao example. Consider fust the correction for thermal output.-. the fifft altemative is gererally preferable. ( I 1) is the acnralstain iaducedby mechanical and/or themal stessesin the test objectat the test temperatue.balance temperahfehavebeenmet. For what might appearto be a more complex case. 6r = semi-corrected strain.analytical expressions for the functions e7s(T) andF(I) can be introduc€dinto theprcglamto permitdfuectcalculatiorof coEected snainsfrom indicatedstains. The compressorspeedis then increasedto N2. e=[4.the changein stess-induced strain causedby the speedincrease. -Fo 2.0. ra .r F" e . Because this requirement is usually ditEcult or impossible to satisfy. thermaloutputat -200p€ t AF(T). )_l r\tz) Tbe same numerical substitution procedule is followed as before.rahlrA f'nm room-temperaturegagefactor +0. Next.( 11).€ r . and the results subtacted to give (€2 . = thermal outPut at temPeraturefl (functional erng) notation is used to avoid double ard tiple subscripB). = l e t . the value used by Miclo-Measurementsin recording the thermal output data. and is thus selected for the following procedure. / ^<\ F C ) = F "' \l 1 + " l = 2 . the gag€factor of the gage at test tempemtue.Undertheseconditions.the strain €l ftom Eq. The engiueer wishes to determine the change in stress-induced straitr causedby ths speedincreasefrom N1 to N2.t ^. (11). assumethe followias.l l - F(\) ^ 'r(4) e1=e1- where: e1 = straiu magnihrde corected for botb thermal output and gage factor variation with tenperature. deviational test ran-.e + . Using Eq.F(4s"c) €1.Applying Eq. (9) as follows: This problem is acb.. Since the gage factor setting of the straitr indicator coincides with that used in measuring the thermal output" this correction can be made by direct subbaction of the thermal output (as giyer otr the gage-packageEngineering Data Sheet) ftom the indicated strain.and hence the double caret ove! the stain symbol. (10) to obtain F(?l).e. tle coEection to the gagefactor at the test tempenture is performed with Eq.-+.rfel]fr F* (l l) Wher the prescribedconditionsotr the gagefaclor setting andthe zero-.(-200t '' -::: = -1587P€ ' 2. ^ l l . .1a1ly no more difficult than the previous example. . 0 7x 1 .07 Test temperature -so. coEected for thermal output only.wiih the temperature of the gageinstallatiooat 11. correction is rnade for the gage factor variation with tempelature. ) Wletr computerizeddata reductiouis used.The secoud and third of the above choices can be used for meaningful stain neasurements orly when the test object is known to be completely ftse of mechanical and thermal stresses at the balancing temperature. and an indicated srrain er.6Vo tFlom ErgirceringDataSheeth gagepackage. urcocected for either thermal output or gage factor variation with teEperah[e. 0 0 6 100/ F(Tt)= 2'sg Substituting itrtoEq.€1). tn €r = [-1850. Combining the two corections.^t e . with a resulting BaBe installatiotr temperamreof 12. i. F(4) = gagefactor at test tempemtue.llrqlcateo stxafr at lest tempefirrure (with inskuloerlt gagefactor set at F*) -1850/r€ fe79(I').consider a strain-gage-itrstrumentedcentri-firgal compressor. That is. aA €t=er-ET/O\t) Strain gage wK-06-2508G-350 Test material Steel tRoom-tempenture gagefactor. -10- rA .As a aumericalexampleof the applicationof Eq.The subtraction can also be doue algebmicaly to yield a si:rgle equation for the strain chatrse: ' ceT T t o (Tz) F(Tz. .tbe indicatedsaaitris a. A-1. (A-1) are givea in Table A-1 for representative adhesives ard gageseries. i.2.WestemRegional Straitr GagECom.Nov.+ hB)JaT + hBdB)-zv A-BaslhA .as = themal expansioncoefEcientsof adhesiveald backing.a thermocouple or resistancetemperahlle sensorshou. (A-1) has b€en evaluated for several represe ative combi. - Fig. The curvature-indicated change in thermal output.APPEI\DIX Surface Curvature Effects on Thermal Outltut TABLE A-1 Arlhesiveand BackingParameters for Usewith Eq.a convexcurvatureis positive. ua-r = 0. = ayeragePoissoa'sratio of adhesive lh. Aeflo lAT.ldbe installed adjacentto the gage.respectively.0 x 10{ (assuminga steel test material). Approximatevaluesfor the adhesiveand backiugparameters fu Eq. (A-1) Fnnk F. an expressionfor estimating the incremental thermal output can be wdtten as follows: A€rrc= (A-1) As an aid in judging tbe approximatemagdtude of the cwvature-induced thermal output. an temperatueis taken infieasein temlreratuefrom thereferencei as positive.ao'o3'R-ir F I tttt I o I ) { givenin Table Because theadhesiveandbackingparameters A-1 areapproximate. The result is aa altered thermal outDut ftom ths data ptovided in tbe gagepackage.Lll+2v ^-B)\hAaA 'wherc. conection may be necessary. the curvature correction defined by Eq.1)whenthe signs of 4I aadR are properly accountedfor . 4e7.-/. Eq. R = radiusof curvatueof testsurfaceat gagesite.Eittee. 11- . Employiug the same basic approach and approximations used by Hines in his derivation.whilea concavecurvatueis negative.in coNistentunits. As a rule of thumb. (A. but generalizing the teatunent to allow for any combinatioq of adhesive and backing properties. tl I .atrdtbe test patt then subjected to test temperatues (wbile ftee of mechanical and thermal stresses)to rccord the "aue" thermal output. 1960. The calculatedresult ftom Eq. 9. In other words.and conespoudingly.that is. dA. Note.4 of the text. With smaller radii. Parametersftom Table A-1 were substitutedinto the equation.the thermal outPut manifested by such ao fustallation is differcnt than for the sarnegage Eounted oB a flat surface. \r . that tho ordinate gives the incremental thermal output per unit d tenperaure charge fiom tj:e idtial referencetemperatwe .lrs = adhesiveaudbackingthicktress. and a decrsasenegative. but it can become signficant when the radius of cuwaturc is very small.When the surfacecurvature is severeenough so that the curvature-inducedincremeutal thermal output may be importart. andbacking. (A-1) evaluatedarulpbfred for vorbas standard Micro-Measurernentsstrain gage backing materials whenbondedto a steelsubstrqte. (A-1) is limited in accuracy.oations of Micro-Measuremetrts adhesivesand gage series. pp.Hines has demonshatedf that whetr a stsaingageis iostalled on a sha4)ly curved surface. h the figure. 1r.along with as = 6.35for all nique and other variables. ze-. the strain gage should be bonded to the test palt as for stai! measuxement. andareaffectedby gageinstallationtechtProceedings.Eq.that is. (A-1) is thenaddedalgebraicailyto the thermaloutp[t datasuppliedin the gagepackageto give the curvatue-corectedthermsl outputfor use in 6aking thermaloutputcoEectioosasshowEin thisTechNote. refeEed to here asthe incrementsl thetmil gutput.A-1 .respectivd as= thermalexpansioncoefEcientof substrate(specimenmatcrial). 4I= temperature chatrgefrom referetrcetemperature. is due to the fact tbat the strain-sensitivegrid of tle gage is above the surface of the test member by the tlLicknessof the gage backing and adhesive layer. dependingupon the required shain-measuemeat accuracy. The curvahre-ilduced ilcremental thermal output is a second-order effect $'hich can ordiuarily be ignored. the incremeqtal thormal output can be neglected when the radius of curvatue is 0-5 it (13 twn) or greater. = survaturr-in4rcedhcremeutalthermalouq)ut. and the results plotted in Fig. It can be shown that under these conditions a tempetaturechangecausesa different strain in the grid than would occur with the grid bondedto a Plane surface.1944.Thesignof the Micro-Measulements incrementalthermaloutputis obtainedftom Eq. the actual thermal output should be measuredas described tn Sectipn 2. 3 Reforence . to thegageinstallerin quickly determinhg As aconvenience the specificsurfacepreparationstepsapplicableto anyparticular test matedal. unlessotherwisenoted. the specific proceduresand techniquesdescribedhere offeranumberof advantages.INC.and.abrading .Simply touchingthe gageswith the fingers(whichare alwayscontaminated)can be detrinentalto bond quality. but for corurbr€ntsuccessin achievinghigh-qualitybonds. It is toward this purposethat the operationsdescribedhereare directed.Lessthorough.Sectiorl 3. adequate ventilation is necessary. and readily reproducible.clean.andexceptiotrs are i:rtroduced as appropriate for c€rtain specialmaterials and situations.Fundamentalto the Micro-Measurenentssystemof surfacepreparationis an understanding of cleanlinessand contamination All open surfacesnot thoroughly andfreshly cleanedmust be consideredcontaminated. andvisiblegagelayoutlinesfor locating and o enting the strain gage..*Theseare. approachesto surfacepreparationmay sometimesyield satisfactory gageinstallations. Furthermore.O. Similarly. step-by-step procedures Jor making successfulttrain gage installalions. To begil with. rcquest Bulletin i18. For morc infonnation. The Micro-Measurements systemof surfacepreparation includesfive basicoperations.tn Section4. following a summary of the general principlesapplicableto the entireprocess.neutrclizins L Micro-Measurements Division MEASUREMENTS GROUP. P.y'. when the instructionsare followed precisely(along with thosefor gageand adhesivehandling).or theinstructor in an educationalinstitution. aswith any materialscontainiagsolvertsor producingvapors. Wl[le a properlypreparedsurfacecanbe achieved in morethan one way. the consistentresult will be strong stablebonds. 1976 *Note: Basic swlace preparotion procedutes dnd techniques are prcsented and described in detail in Micro-Measuremehts' YideoTech" Library.feclran 2. Theimportanceofattentionto detail. It is ryorth notirg that strain gagesas receiyed ftom Micro-Measurements are chemicallyclean.conditioning .and uncontaminated.0BASIC SURFACEPREPARATION oPERATIONSAND TECHNIQUES 2.hichshould cussesspecialprecautionsand considerations be borne in mind when working with unusualmaterials and/or surfaceconditions.properly.aDdpreciseadherence to instructions.Sectbr. I. theyconstitute a carefullydevelopedand thoroughlyprovensystem. Aaleigh. it is imperativethat the materials usedin the surfacepreparationbe fresh.in theusualorder of execution: Thesefive operationsarevaried and modifiedfor compati bility with differenttestmaterialproperties.o hcludes a chart listing approximately75 common(anduncommon)materialsatrd the corresponding surfacepreparatiotrtreatments.1General Principles of Surface Preparalion for Shain GageBonding The purposeof surfacepreparationis to developa chemically cleansurfacehaving a roughnessappropriateto the gageinstallationrequirements. can prepareindividual proceduresheetsfor particular materialsof iaterest.0.The proceduresare simpleto Iearn. The surfacepreparationoperationsare describedindividually ir .() INTRODUCTION Straingagescanbesatisfactorilybondedto almostanysolid material if the material surfaceis prepared. and require cleaningimmediately pdor to gagebonding. These videotape tequencesprcvide thorough.Of course.or evencasual. . generallylow in toxicity.andthe relevantinformationfrom this InstructionBulletin transfered to the blank spaces to producea completelyspelled-outsurfacepreparationprocedure for any material lisled.The form canbe copied.application of gagelayout lines .l t Surlace Preparation forStrainGage Bonding . (919)365-3800 Telephone Telex802-502 FAX(919)365-3945 MEASUBEMEI{TS GROUP Printedin USA ..0.lnc. easyto perform. On the backcoverof this InstructionBulletin.NC 27611. .0 dis'i.a blankform is providedsothat the laboratorysupervisor.and speciallytreatedon theundersideto promoteadhesion.a surfacealkalinity correspondingto a pH of7 or so.cannotbe overstressed ir: surfacepreparation for straingagebonding.Box 27777.USA ooopyright Measurements Group. ard do not requirespecialventilationsystemsor other stringent safetymeasures.solvent degreasing .themethodsgivenherecanbe recommendedwithout qualification. 2.the surfacepreparationmaterialsusedir these proceduresare. )Finish abradingis done with silicongrit . .if physicallypracticable.63 0:4. and castalumiaummay requireheatingto drive off absorbedhydrocarbonsor other liquids. the air supplyshouldbewelifilteredto removeoil andother contaminantvaporscomingfrom the air compressor. 2. In anycase.or wiping with GC-6 Isopropyl -.thesurface. Following are severalexamplesof surfacerecontamiaationto be aYoided: . Conditioner A is a mildly acidic solution which generallyaccelerates the cleaningprocessand. If gdt blasting is usedinsteadof abrading.It is also imPortart to guard against .it is good practiceto approachthe surface preparation task with freshly washedhands. see Section 3.4 cross-natched '16.or safetyprecautions.. In eithercase.In contrast. are used for fansducer installations. triangularindexmark definingthe longitudinalandtransverseaxesofthe grid are alignedwith the referencelines on the testsurface. Dragging coDtaminantsitrto tbe cleanedarea from the uncleasedboundary of that area. --. The ootinum surface finish for gage bondiDg depends somelihatuoorthe natureand purposeof the installation..For rough. -J saryto startwith a grinder. b. an ultrasonicallyagitatedliquid bath.a rougher (and preferablycross-hatched) surfaceshouldbe prepared. However.4 WetAbrading WheneverM-PrepConditionerAis compatiblewith thetest material(seeSection4.In preparationfor gageinstallationthesurfaceis abradedto removeany looselybondedadh€rents(scale.organic .the chanceof recoataminationin subsequeDt andwill providean areaadequatelylargefor applyingprotectivecoatingsin the linal stageof gageinstallation.3 SurfaceAbrading General .or reushga once-usedsurfaceof the sponge(or of a cotton swab). Whenever Iu thecaseoflargebulkyobjectswhichcannotbecompletely an areacovering4 to 6 in f100to 150mm) on all degreased.oxides. TABLEI CLASSOF INSTALLATION Generalstressanalysis Highelongation Transducers Ceramiccement SURFACEFlNtSH.The linesaremadeperpendicumeasurement lar to oneanother. and has the advantageover rougher surfacesthat it can be cleanedmore easily and thoroughly. '- 2.The abradingoperationcanb€ " performedin a varietyof ways. cleanlinessis vital throughout the surface preparationprocess. below. Smoother surfaces.Alcohol.l >6.discsander. As noted earlier. contaminants.). e.etc. castiron. * Degreasingcanbeaccomplishedusingahot vaPordegreaser.The grit usedin blastingshouldnot be recycledor usedagainin surfacepreparation for bonding strain gages. .either clean aluminaorsilica(100to 400grit) is satisfactory. For generalitressanalysisapplications.Degreasilg shouldalwaysbe thefrrst operation. and to wash .-.a relativelysmooth surface(in the order of 100.actsasa gentleetchaot. The referenceor layout lines shouldbe made with a tool whichburnishes . One-wayapplicators. Porous materialssuchastitaniud.4 Gage-LocationLaYout Lines The normal methodof accuratelylocatingand orientinga strain gageon the test surfaceis to first mark the surfacewith a pair ofcrossedreferencelhes at tbe poiDtwherethe strain is to be made.a 4H drafting pencil is a satisfactoryand convenientburnishing tool. Wiping back andforth with a gauzesponge. on some for materials.1. theentle testpieceshouldbedegreased. and soluble chemical residues.handsasneededduringthe procedure.0). paint.ortie.6 >250 >6.suchasthe aerosoltype.On theseand other hard alloys. c. sidesofthe gageareashouldbe cleaned.with oneline orientedin the directionof The gageis then installedso that the strain measurement.or wood. aerosoltype spray cansof CSM-I Degreaser. ratherthanscoresor scribes. On aluminumand most othernonfenousalloys.or coarsesurfaces. rm9 Pln lJm 63 . Layoutlinesare ordinarily applied following the abrading operatior and beforefinal cleaning. a. Allowing a cleanedsurface to sit for more than a few minuies before gageinstallation.125 1. recontamination of a once-cleanedsurface. Bcyondthe above.andto developa surface texturesuitablefor bonding. The recommendedsurfacefinishesfor severalclassesof gage installationsare summarizedin Table I.2 >2s0 .(Note:Before perfurmtng any abrading operations.This is to avoidhaving * subsequentabrading operationsdrive surfacecontaminauts into the surfacematerial. useon rnagnesium.ile keepingthesurfacewetwith thissolution.A scribedlinemayraisea burr or createaslressconcentration.of cteaning solvents are always preferable becausedissolved camot becarriedbackintotheparentsolvent.Al1lesiduefrom the burnishingoperation shouldberemovedby scrubbingwith ConditionerA as describedin the following section.rust. or 2'5 lrm. compatiblewith the thitr "gluelines"requiredfor -i"i-um creep.This will minimize operations. d. 2.3.sucha line can be detrimentalto strain gage performanceand to the fatigue life of the test paft.0. greases. rms)is suitable. contaminants possible.2 SolventDegeasing Degreasingis performedto removeoils.1 f.graphitepencilsshould neverbe usedon hightemperaturealloyswherethe operatingtemperaturemight causea carbonembrittlementproblem.rin. andrecommended * sizesfor specificmaterialsare given in Section 4. Allowiag a cleaningsolution to evaporateon the surface. Touching the cleanedsurfacewith the fiDgers.6. carbidepaperofthe appropriategrit.It is not recommended syntheticrubber.burnishedalignmentmarkscanbe madewith a ballpointpenor around-pointedbrassrod.dependingupon the initial condition of the surfaceand the desired{inish for gage it maybe necesiqstallation.theabradingshouldbedonewh. or allowing a partially prepared surface to sit between steps in the cleaning procedure. when very high elongationsmust be measured. galvanizedcoatings. biotting with gauzespong€s.In orderto developa proper substratefor gagebonding.Ofor bonding gagesto epoxies.it is necessaryto apply a leveling and sealing Precoatof epoxy adhesiveto the concrete'Beforeapplyingthe precoat.accordingto the procedure specifiedin .'tection 4. Whendealing with toxic malerials such as beryllium.andthenthe surfaceshouldbe rinsedthoroughlywith cleanwater. ' 2.and scrubbiag the surfacewith a cleancotton-tiPpedapplicator. recontamination If the foregoinginstructionsarefollowedprecisely. the surfaceshould be dried by wipingihrough the cleanedareawith a sinSlaslowstrokeof a gauzesponge.thesurfaceis now properlypreparedfor gagebonding.0. UseoJSolvents on Plastics Plasticsvary widely in their reactivityto solventssuchas thoseemployedin the surfacePreparationproceduresdescribedhere. ContaminatedCond! tionerA shouldbe blottedwith gauzesponges. vihen clean.with afreshsponge. and the Plastic.{ throug}out this operation.Whenit is not permissibleto removethe plating. the epoxysurfaceis cleaned and preparedconventionally. A final thorough rinse with distilled water is usefulto removethe residual tracesof 'rater-solublecleaningsolutions'Beforeprecoating.1 SafetYPrecautions As in anytechnicalactivity.the concretesurfacemust be Preparedby a procedurewhich accountsfor the porosity of this material. it will be necessary surfacewith a higher temperatureresin systemsuch as M-Bond GA-61. In applyingthe coatingto the porousmaterial. Surface irregularities can be rerooved by wire brushing.2.and the surfacescrubbedwith cottontipied applicatoriuntil a cleantip is no longerdiscoloredby tUescrubUing.if this is permissible.0 to 7. are particularlysubjectto creep. uranium. a single slow stroke of a clean gauzesponge'with a fresh sponge.Then. M-Prep Neutralizer 5A to the cleanedsurface.plated surfacesare detrimentalto strain gage stability. Plated Surfaees In general. Tbe next stepis to applyM-Prep ConditionerA generously to the surfacein and around the gaging area.Seclricn4. and leveledto form a smoothsurface. etc' all proceduresandsafetymeasures shouldbeapprovedby thesafetyofficerof theestablishment before commencingsurfaceprepardtion' 3.Sectiaz4. \r'hicb is suitable for all Micro-Measurementsstrai[ gage This shouldbe doneby libelally applying adhesivesystems. disc sanding.Warming the surfacegentlywith a propanetorcb or electdcheatgun will hastenevaporation.and evenharderplatings ofthe imperfectbondbetweentheplating maycreepbecause andthe basemetal.beginaingwith thecleanedareato avoid from the uncleanedboundary.For referredto for the recommended manufacturer of the the plastics not listed in . and it is preferableto removethe plating at the gage Cadmiumand nickelplating location. or +9JoC). and scrub the areawith a stiff-bristledbrush.During this processthe surfaceshouldbekept constantly wetwith Conditioner A until the cleaningis comnleted. or grit blasting.When the adhesiveis completelycured.The spongeshouldneverbe wiped back and forth.and rinsing with water.For thosecasesia whichthetesttemperaturemay exceedthe specifiedmaxioum operatingtemperaturcof to fill the AE-10 (+200'F. and other Codtaminationfrom oils.6 Neutralizing The final step ia surfacepreparation is to britrg the surface conditionback to an optimum alkalinity of 7.ieclioz r'.The stroke should begil i:rside the cleaned areato avoid draggiagcontaminadtsin from the boundary ofthe area.the cleanedsurfacemustbethoroughlydried. sincethis may redepositthe contaminants on the cleanedsurface.The cleanedsurfaceshouldbe kept completelywet with Neutralizer 5.plutonium.ConditionerA shouldbe aooliedrepeatedly.5 Surface Conditioning if After the layout liDesaremarked.whengrinding. mild detergent and a brush bristled then rinsed with clean water. the surfaceshould be preparedaccordingto the proceduregiven in .rough.andporous. the oDeratorshould wear safety glassesand take such other safetyprecautionsasspecifiedby his organizationor by the OccupitionalSafetyand HealthAdministration(OSHA).2 SurfacesRequiring SpecialTreatment Conaete Concretesurfacesareusuallyuneven.shouldbe compatiblesolvent.it should be abradeduntil the basematerial beginsto be exposedagain.the surfaceaciditymust be reduced by scrubbing with M-Prep Neutralizer 5. plant $owth. scrubbingwith a stiffvigorous by soilsshouldbe removed The surfaceis solution.or filing.andthegage or gagesshouldbe installedassoonaspossible. M-Bond AE-10 room-temperatureMicro-Measurements is anidealmaterialfor precoatingthe curingepoxyadhesive concrete.Followingthis.Following the water rinse. afterwhich all loosedustshouldbe blown or brushedfrom the surface. which includesmost commonplastics.5pH. When neutralized.a singleslowstrokeis madein the oppositedirection.0SPECIAL PRECAUTIONS AND CONSIDERATIONS 3. greases.0.Cleaninssolutionsshould neverbe allowedto dry on ih" srrface. For example.discsanding.safetyshouldalwaysbea prime considerationin surfacepreparationfor strain gagebonding.Note that it may be necessary procedures to minimizethe effectsof creep.0 for the specfic plaring to adjust testing involved.Beforeapplyinga solventto any plastic.the adhesive should be worked into any voids. lead.the surfacesbouldbe driedby wiping throughthe cleanedarea with. solvent the between to verify nonreactivity .{. be performed should tests or materialshoulclbe consulted.a sinSlestroke should then be madein the oppositediTection. 3. 8-130.and unaffectedby mostsolvents.nants to remove.reliable and fit Jor the purposesfor which recommmded. Surfacepreparationproceduresfor other materials are defined similady in the table. operations. procedure for any particular material. expressedor implied. to the bestknowledge of Micro-Measurements. but no warranty.or damage. In oxidize rapidly.quick access to the rials.and chemicalagents recommendedin this InstructionBulletin are. Regardlessof efforts to avoid silicones. the effect on the static mechanicalproperties of the test part is usually ncgligible comparedto other error sourcesin tbe experiment.'The Alcohol column indicatesthat this is a suitablesubstitute operation.because in the Grit B/ast columa.assumethat the necessityarisesfor bonding one or more strain gagesto a brasstestspecimen. in many cases.0INDEX OF TEST MATERIALS AND SURFACEPREPARATION PROCEDURES Ordiaarily. nor shall Micro'Measurementsbe liablefor any injury.the specificstep-by-step proceduresare given for approximately 75 different mateand convenietrt.Thefourth andfifth operationsconsistof applyiaglayout linesfor locatingthe gages.andscrubbingthe surfacecleanwith ConditionerA.that renoval of a platedor hardenedsurfacelayer. Struin Gage Installations with M-Bond 200 Adhesive.many hand creamsand cosmetics containsilicones.director consequential.it is recommendedthat the gagesbe installed \4.preferablyheatedto +200oF (+95'C).Light contaminationcansometimes by cleaningwith ConditonerA.In the third operationthe speci.from ABS Plasticsto Zirconium. Evenin the caseof finite materialremoval. gageinstaller is specfically advisednot to substitutegrii blastingfor other surfaceabradingmethods. 8-137. and to environmental quality.connectedwith the useof the information' Before applying the procedures to any matefial the user is urged to carefully review the application with respect to human heahh and safety.recommendationsfor which shouldbe obtainedfrom the manufacturerof the silicone compoundinvolvedin the contamination.Continuingacrosstherow.The problem is compoundedby the high natural affinity of the siliconesfor most materials.This may not be as easyas it sounds.nformation is presentedin chart form in Table II.nof Table II to Brass.may noticeablyaffectthe fatiguelife or the wearcharacteristicsof thepart whedoperatedunderdynamicserviceconditions. Similarly. thesecond degreasiag operationcallsfor abradingthe specimensurfac€with 320grit silicon-carbidepaper.Reading down the SpecimenMaterial coluro. or of a surfacelayer with significant residual stresses. Intbe Remarlcscolumn. and following that ro\y affoss the table to the right. IMPORTANT NOTICE Additional ReJerences For additionalhformation. The test materials are listed alphabetically.For instance.sincesiliconesare relatively inert chemically. refer to Micro-Measurements Instruction Bulletins listed below: 8-127. the sirrfacepreparation proceduresdescribedin this Instruction Bulletin will not causemeasurabledimensional changesor otherwisealter the mechanicalcondition or stateof str$s in the test part. For compactness.andtheseshouldnot be usedby persons involved in gageinstallation.Dimensional or Mechanical Changes Due to Sulace PrePuation 4.and the completeprocedurefor eachmaterialis definedby oneor moredigits in eachofthe applicableoperationscolumnsof the table. The bestpracticeis to keepthe gage-bondingareafree of silicones. is given.sincethe widely usedsiliconescan be introducedfrom a vadety of sources. the first the specistepin surfacepreparationconsistsof degreasing symbol(1)in theIsopropyl menwith CSM-l Degreaser. For example.accompaniedby specialwamingsor recommendationsin the Rernarkscolumn. and. Silicone Contamination The propertiesofsiliconeswhich makethem exceuentlubricanti andnold-releaseagentsalsomakethen the enemiesof adhesion. Someof the machining lubricantsalsocontainsilicones.WhenaDoperationnot includedin the first ten column headingsis required.paPer.they are among the most difficult surface contami.in order to avoid significantly altering the surfacecondition of this relatively soft material.and suchlubricantsshouldbe avoidedwhen machiningparts that are to havestrain gages installed.it is indexedin the Orler column.contamination may be removed still occur.This information on surfacepreparation for strain gage bonding is presented in good faith as an aid to the strain gage installer.It should be borne in miad.with an affow pointingto the Rernarkscolumnwherethe operationis specified.ithin 20 minutes after completilg the surface tbefreshlybaredbrasssurfacetendsto preparation. Strain GageApplications with M-Bond AE l0l15 and M-Bond GA-2 Adhesive Slstems.and by their tetrdencyto migrate. . surfacepreparation In this section. the addition. The procedures.Furthermore.loss. silicone-saturatedcleaning tissuesfor areaorby eyeglasses shouldnot beusedin thegage-bonding gage-installationpersoDnel. Morc severecasesmay require specialcleaning solutions and procedures. the i. Cleaningwith isopropylalcoholis the final operationin the procedure. Strain GageInstallations with M'Bond 43'B' 600' and 610Adhesives.and thereforePotentially the most seriousof contamhants to beencounteredia the practiceof bonding strain gages.wet men is reabradedwith 400-gritsilicon-carbide lappingwith ConditionerA iffeasible. Each digit identifres the required operation and specifiesthe stepnumberfor that operationin the complete procedure. however. p9gE u? N @ a.14 T J -=^-^ :o L EE.E'.:2 i i'.:". t . IgI E EFEq A -o .- | 3 @ o) ! : E E t g-P :o6a -EE i E E P*Eoi6 .: .F :EEe* € E5 E) E . o c lu lo o = J o !J J F !J = z 2 o !I t0 ..nt E Er . !^. s: :6 <d -EE:E! 9+ . = o o o = = j 2 = = = J ul F J UJ = ul ut [t F = 2 J J E F z o. F E S# b & q) .5E T€ES Er 6 .c 99. ii. 5Edi5* . E :. F t! = z LI = o u.!= S E E . 9= EH.q.6 -9i € * ! E' >:. Ee : E99 " eii6e. * 1 8E a.{ iii5]Y'i E E Y P:+ F€+ :6 i9 g3E 3 fii:. |rI h9 UJ N J o J o F 6 o E o j z = - z = :' z = o F (.E A . o !l at.1 tu z o o o . 30 . gE =v t E FXo ti< F.o E: -. e 3 Es EEsE F x69E. T L: =Ei6:: t a -: =. 6l <! -- 6l 6l _q z z z a z z z z z.Q-E F= q <6 E>. z \ o o J . E -r€ie EsFFa .D z o t. ||l _=E ! :9 -E E*Pd 5.l ut 3 <go] -q€ d P:6 3 drE i rxri _._ . : ?2 . F:3 o e .: . I 6X 3 3.' ..69 i. oR *. at) a z lvt ct. l'F z J o l! a.i s.Y !g I EE piE ef Ee'3 . : (. Y o E l0 o |rJ N 2 o = = o o z F o tt z I = = = E uJ o a o |l..r.t E? Et 6! N .E a ul o. . i9 I 9:.1 N J = z F J o . cr- tlo tr: i o lrl F = z |rl = ul a q uJ u. a fi3.98 . E gE tm b..1 o o J = = = = z z z z o..1 F o o Y o uI z ul = = z z = z = o ltl 2 |rJ J ql to l! F a z = z z z o J J !.< zQ. J (5 z z o E 2 z z E = o tr o 2 !. i'E '6c E: :< :: E LTJ o.9E ? ts*.r Fr J. J UI 2 o E J tu Y o (. )2 5 E:.t^ =2 5 o e'' 5 .e€ 6 E E :> EsEFo EE g: E.18 q : ! . E : €s E . I o..i. 9! 3 ' s:g*€i 9-ct c EEgEEiE 3 3 E o c t:6 €i.9 z q' 9.i c .l F !l F tt F = = o F z J ul to o o u.l J E !r g zur o ul tt J ul = o z v I z rt z o : o s F ul J gl E 4.E:* ll ' ' E E !-< E+ ?2 E -z t/) a :E i:o (!= ai N E-g Ut tr @ N ro rt) . E:-: t . I |l. F! ' 5 = o J s +. (\l 6l N N at) o 6l ol N 6l N N 6l z t! o z z a ur tr Q E 9E 3 hP . r! OE. -cx .1 ||.9 ! YT .9e {.E !J E It o (. o o o z N N .E E . o l! = o J gJ gt F o J lll u.E:* L'I :3E : 6-: !6 g: :6 ot '. Co.r') 6t N 6l ol C\l 6l 6l 6l z (\l z o 34 x3€ ' .1 F o gt ||. 6r_ = 8E? o '3 *(\1 +:o. E E-.Je 5 6> 'lll ...5 6E = .isEaE3 o t! F o z o ul an o ! 9: t ' a t ' t tr .*8 :€EE ()=o b orf E 5E ! ..1 F 2 !I o o o J ul ltl F o u.69 ? @ z z . . r I t c z o z 9 F 4.l E =o:-j < 3 E _:€sEbi .: ' :j8 9= i6 co. 3 I art ! a o !) E d .l Io t o r f J o E o J J z J J s J uJ !j o zut @ t B .:! ! i W . rr- E.6 trl z tII J o lr. z lll F : o z at 3 z F F = = 2 E = o o .9e rEEF Eiex 6-oP z6 .c .l o ul z o F o J 3 z F = f 2 o J tt t|l F z = t- F tr !t @- = o 4. a -J3 c = iT I .! tEe + :7 o.E. E:?Eg Ef gIg FE€ fE3i9E = a gE :{-J t in .lnE i< . g! Et u.8 lre 5 =E g- u J .9 O Ei. 3e a 3> P' >.) = o gt q o tr9 Q z!l E uJ = zul - !l o o ||J F = 2 o F J ltl |rl z z z o o tu J F gI F tr.4'^ E: s F z lll I EiE-iE f im.l t- z(rl 7 ||.: Edr -_< 66-:i i= e ..tlll -a .9t i! E 39 5a tr9 + '3 d'q gF !.S iiE uJ ol (\l C\I -q- FE Es e5 E' tt) . Date Prepared FORSTRAINGAGEBONDING PREPARATION SURFACE SUPPLIES: REOUIREO D.atlons): suRFACEpRgpARATtONOPERATIONS t. . (do nol onlt or modlly. Inslallstraingagespromptlyaftercompleting .Procadure No.or chang€tho sequonceot ope. o 4.ny operallons. NOTE thesurfacepreparation.takethe necessarystepsto ensurea cleanworkingenvironment. . 7. ANO PNECAUTIONS: SPECIALINSTRUCTIONS NOTE Beforebeginningthe followingprocedure. 4 Reference . EA N2A. EA M-Bond Adhesiveh CEA.43-B WA.J2A 200or AE-10or AE-15 AE-15 o. TA.) Type ofTest or Applicatlon Gencralstadc oa strric-dynamic sress analysis High elongatioo (postyield) Dynamic(cyclic) strEssanalysis Transdtrcctgaging t SecTable7.sA. b Se! Table7. 450 6t0.4 RecommendedAdhesives tor Difturent Strain cage Series (CourtesyMeasurementscroup.iss.wK. J5K 6IO.wK. Operatirg Temperature Rang6.sA. CEA. Inc.3. sK.-' I I 332 STRUCTURAL MOOELING ANDEXPERIMENTAL IECHNIOUES Table 7. J5K wK.sK wA."C -45 to +65 -45 to +205 -259 to +230 -45 ro +65 -75 to +65 -195 to +250 -45 ro +65 +5 to +95 -45 ro +150 -195 to +175 M-M GageSe.5.EA 8P ED WD WD CEA.450 wA.610 600or 610 6t0 6t0 200or AE-l0 AE-15or AE-l2 200or AE-10 AE-10or AE-l5 600or 610 AE-10or AE-15 600or 610o. SA. TK.sK WK. TK.SK WK .) J l J J l I I I I i J I J I . .'r. and (3) me 'with adequate ventilation.il:*.8ox27777.Imuediate bonding of eye. il. For additional health and safety information.1.g. Division Micro-Measurements GROUP.wllen bondingto plastics. Yarious installation techniques are described on pro' fessionally prepared videotapes available from the MeasurementsGroup. (2) avoid prolonged or repeatedbreathing of vapars.age-embrittlement l-7 control.:. Request Bulletin 318 for details. Refrigemtion after oDeninsis not recommended.care shouldbe takel to ensurethat the M-Bond 200 hasreturnedto room-temperatureequilibrium before opening.e. The user is cautionedto: (1) avoid contact with skin. -i:'.Thenorrangeis -25'to +150"F (-30" to mal operatingtemperarure 2 0 0 i s c o m p a t i b l ew i t h a l l M i c r o +65'C).185"C).Raleigh.for one-cycleproof teststo over+200"F(+95"CJor to below-300"F (-.1.". Life can be extended if upon receiPt the unopened material is refrigerated [+40'F (+J'C]1. HANDLING PRECAUTIONS M-Bond 200 is a modified alkyl cyanoacrylatecom' pound. particularly if exposed to elevated temPerat[res For theser€asons. adequateprotectivecoatingsare essential This adhesivewill gradually become harder and more britde with time. it shouldbe appliedto surfaces of +70oand+85'F (+20" to +30"C).l".1979 "CopyrightMeasurements tfjgieii'S:ib-. M-Bond straiBgagesandmostcommonstructuralmateMeasurements rials. Due to possible condensation problems which will degradeadhesiveperformance.. SIIELF AND STORAGE LIFE UnooenedM-Bond 200 adhesivehas a shelf life of nine mon[hs when stored under normal laboratory conditiom.it shouldbe notedthatfor best performance.1t:j::t-'-.:-'r'l Telephone 365-3800 I {919) FAX(919)365-3945 J Printedin USA by PP .r:*':.extendedsolvent the adhesive. ITIEASUREMENTS NC27611.The catalystshouldbe used sparinglyfor bestresults.i:ljji*:::.. . Group. Causesirritation.for fatiguestudies...lNC.J. the procedures and techniques presented in this bulletin should be us€d with qualified Micro-Measurements installation accessory products (refer to Micro-Measurements Catalog A-110.:r::'l::'.1.Excessivecatalystcan contdbute of manyproblems.l:.USA P..etc.7 200Adhesive withM'Bond Installations Gage Strain INTRODUCTION CertifiedM-Bond 200 is an excellent Micro-Measurements of its fastroombecause general-purpose laboratoryadhesive When application.poorbondsuength.:r . skin or mouth nay result upott contact.O.For besr reliability.Inc. thetemperatures between environmettof 30Eato 659o..M-Bond200 dled and usedwith the appropriate can be usedfor high-elongationtestsin excessof 60 000 microstrain. and ease of cure temperatue ProPerlyhanstraingage.:.Mhumidity andin a relative Bond200catalysthasbeenspeciallyformulatedto controlthe reactivityrate of this adhesive. the adhesiveflowout shouldbe kept to a minimurn.poor gluelinethickness evaoorationtime requiremenE.:-l:t'. consult the material safety data sheetwhich is availableuPonrequest For proper results..M-Bond 200 is not generallyrecommendedfor installationsexceedingone or two years. M-IINE accessori€sused in this procedure are: CSM-1Degreaseror GC-6IsopropylAlcohol SiliconCarbidePaper M-Prep Conditioter A M-PrepNeutralizer5A GSP-I GauzeSponges CSP-1CottonApplicators PCT-2A CellophaneTape )- -:. Since M-Bond 200 bonds are weakenedby exposureto high humidity. place the gage (bonding side down) on a chemically clean glass plate or gage box surface. Remove all residueand Conditionerby again slowly wiping through with a gauze sponge. Step 2 Preliminary dry abradingwith 220. bwi. (do not sciDe) whateveralignmentmarks arc neededon the specimen. Place a 4.. With a single.thus the use of "one-way" containers. is highly advisable. Step 1 Tholoughly degreasethe gaging areawith a solvent.6 ntm) should be left between the gage backing and terminal. but there are some materials (e. and lists specific considerations which are helpful when working with most common structuralmaterials.to 150-mm) piece of MicroMeasurementsNo. 4.then dry by slowly wiping through with a gauze sponge.or 320-grit silicon-carbidepaper (Fig.position it on the plate adjacelt to the gage as shown. The former is preferred. .Repeatthis wet abradingprocess.See Fig. titanium and many plastics)which rcact with chlorinatedsolveflts.to 6-ir' (100.such as aerosolca[s. Take care to center the gageon the tape. Step 3 Now appty a liberal amount of M-Prep Neutralizer 5.Do nol wipe back and forth becausethis may allow contaminantsto be redeposited.In thesecasesGC-6 Isopropyl Alcohol should be considered.or 400-grit silicon-carbide paper on surfacesthoroughly wetted with M-Prep Conditioner A. A spaceof approximately l/16 it (1.Repeatedlyapply M-Prep Conditioner A and scrub with cotton-tipped applicatorsuntil a clean tip is ro longer discolored. slow wiping motion of a -sauzesponge. 2a) is generallyrequired if therc is any surfacescaleor oxide.sh. Carefully lift the tape at a shallow angle (about 45 degrees to specimen surface).as in Fig.Never allow any solution to dry on the surface becausethis invariably leavesa contaminatingfilm and reduces chancesof a good bond. bringiag the gageup with the tapeas illustratedin Fig. 1). Micro-Measureruents 'Instruction Bulletin B-129 presentsrecommendedprocedures for surface preparation. 3. Step 4 Using tweezersto remove the gage from the mylar envelope. such as CSM-1 Degreaseror GC-6 Isopropyl Alcohol (Fig. With a 4H pencil (on aluminum) or a ballpoint Pen (on steel). Final abrading is done by using 320.GAGE APPLICATION TECHMQUES The installationprocedurepresentedon this and the following Pages is somewhatabbreviatedand is intendedonly as a guide in achieving proper gage installation with M-Bond 200.carefully dry this surface.{ and scrub with a cotton-tippedapplicator. PCT-2A cellophanetape over the gage and terminal.9. 2b.All degreasingshould be done with uncontaminatedsolvents . this is followed by wiping dry wjth a gauzesponge.If a solder terminal is to be incor?orated. Step 8 t Lift the tucked-undertape end of the assembly. holding in the sameposition.9. the back d any gage can be cleanetl with o cofton-tipped applicator slightly moistened with M-Prep Neutralizer5A.and. M-Bond 200 adhesivewill hardenwithout the catalyst. 6b) so that the gage and terminal lie flat. Very little catalystis needed and should be applied in a thin. and I0 beforeproceeding. PCT-2A cellophane tape is usedbecausethis tapewill retain its mastic when removed. and firmly anchor down at least one end of the tape to the sPecimen. apply one or two droPsof M-Bond 200 adhesiveat the fold formed by the junction of the tape and specimen surface (Fig./tape on the gage are over the layout lines on the specimen(Fig. with the bonding surfaceexposed. Continue lifting the tape until it is free from the specimenapproximatelyIl2 in ( I0 nm) beyondthe terminal. Step 7 M-Bond 200 catalyst can now be applied to the bonding surfaceof the gageand terminal.Allow the catalystto dry at leastone minute under normal ambientconditionsof +75'F (+24'C) and30Vato 659orehtive humidity beforeproceeding. If contaminated. 8).but less quickly and reliably. 6a).Step 5 I assemblyso that the triangle alignmentmark Position the gage. Step 6 Lift the gage end of the tape assembly at a shallow angle to the specimen surface (about 45 de$ees) until the gage ard terminal are free of the specimen surface (Fig.ReadSteps8. Lift the brush-caPout of the catalyst bottle and wipe the brush approximately 10 strokes againstthe tip of the bortle to wring out most of the catalyst. .will not cause unevenessin the gageglueline.lift one end of the taPeat a shallow angle until the assemblyis free of the specimen'Realignproperly. Note: Micro-Measurements gages have been treated for optimun bonding conditions and require no pre-cleaning before use unless contominatetl during handling. If the assemblyappearsto be rnisaligned. This adhesiveapplication should be aPproximatelyl/2 in (iJ mn) outside the actual gage installation area.taking place when the adhesivecomesin coatact with the specimensurface. Move the brush to the adjacent tapeareaprior to lifting from the surface.but slide the brushover the entirc gage surfaceand then the terminal. Note: The next three steps rLtstbe completed in the sequenceslrcwn. Do not sfoke the brushin a painting style. uniform coat. 5). Tuck the loose end of the tape under and Press to the specimen surface (Fig. This will insure that local polymerization. within 3 to 5 seconds.7). Realig[ment can be done without fear of contamination by the tape mastic if Micro-MeasurementsNo.Set the brushdown on the gageand swab the gage backing (Fig. Remove the solder flux wirh M'LINE Rosin Solvent' J- RSK.To remove the tape.Prior to any soldering operations. Iackof "thumbheat"which helpsto speedadhesive Waittwo minutesbeforercmovingtape. uniform layer of adhesiveis desiredfor optimum bond performance.It is not necessaryto remove the taPe immediately after gage installation.thispressure extendedto severalminutes. pull it back directly over itselt. Step10 Immediatelyupon completionof wipe-outof the adhesive. Selectappropriatesolder.Wherelargegagesare involved. FINAL INSTALLATION PROCEDURE 1 .or it may be wherecurvedsqrfacessuch as fillets are encountered.Step 9 ImmediateLyrotate the tape to aPProxiriately a 30-degreeangle so that the gage is bridged over the installationarea. Selectand apply protectivecoatingaccordingto the Protective coadng selectionchart found h Micro'Measurente ts CatalogA-110.In low is humidityconditions(below3070)or if the ambienttemPerature timemayhaveto be application below+70'F (+20"C).firm thumbpressuremust be appliedto the gageand terminalarea (Fig. o ./tapeassemblywith a piece of gauze (Fig.refening to Micro-Measurements Catalog A-l 10. Step 11 The gage and terminal strip are now solidly bondedin place. This technique will Prevent possiblelifting of the foil on open-facedgagesor other damageto the installation.Thispressure shouldbeheldfdr at leastoneminute. 2. 10). Prcssure-application polymerization. and attachleadwires.While holding the tapeslightly taut. I l). slowly andJirmly makea singlewiPing strokeover the gage.The tape will offer mechanicalprotectiontbt the grid surfaceand may be left in place until it is removedfor gage wirins. A very thin.Use a frm pressure with your fingers when wiPirg over the gage. 9) bringing the gage back dowrl over the alignment marks on the specimen.open-facedgage grids should be maskedwith PDT-I drafting tapeto preventPossibledamage. peeling it slowly and steadily off the surface (Fig. padding the oPerapressure dudng preformed to use advantageous due to the time shouldagainbe extended tion.I. 5 Reference . Thesesoldering uniti are widely used by professional strain gage installers everywhere.e. Moreover. Use of impropermaterialsor techniquescan significantlydegrade straingageperformance.in both sress analysislaboratoriesand in tlansducer manufacturE.g.they are low in cost.brazing. Haleigh. Design of the solderingpencil also requiresspecialcoosideration.Thesereliable.Inc. making soldering much more difficult. availablein variousalloy compositions in the form of obtained easily and are temperatures. It should be light in weight. proceThepurposeof this TechTip is to outlinerecommended durei andmaterialsfor attachingleadwiresto stain gagesolder tabsor to bondedPrinted-circuitterminals.andofferanexcellentcombination properties.but also to allow for environmental conditions such as drafts or outdoor solderingin cold weather.1985 Measurements @Copyright . Othermethods. and thus make it more difficult to achieve a proper joint.Power-confiolled to thesoldertemPenture provideslow voltageandadjustable directly solderingiron.in wire form. rcquirementsare severein the senseof approachingthe limits of the strain gagecircuit capabilities. tools.andconductive able. chisel. MEASUFEMENTS P. appropriate donewith This is particularlytlue whentest accuatestrainmeasurement. They arc conveofelectdcaland nientto use. mechanical it mustbe Althoughsolderingis basicallya simpleprocedure.O.but find only limited application.' long-termstability' high-elongationmeasuements. and with the gripping area thermally insulated from the heating element. melting either solid wire or wire with a core of flux.suchas spot welding.to accommodate the melting points of the different solders commonly usedfor straingage connections. and minimize operator fatigue cluring long periods of use.of course. connected ing iron tip.fatigueendurance'etc. the bonding adhesive. M-rINg soldersandinstallation Measurements SOLDERING STATION AND PENCIL to it is alwaysnecessary Forprecisionsolderingof straingages. while offering greater surface area for better heat transfer and morc effective soldering.pastesoldem. flat tiPs act to confine the solder.becausethey tendto draw solderawayfrom the work arca. with a very flexible power cord. genqrally.For thesereasons. that station soldering or usea temperature. ease. and to instantly vaporize the flux.Soldershavemany for stnin gageuse. is not ordinarily suitable for strain gage use becausl the tip temperahre is aPt to be far too high. to assule techniques and suPPlies.The temperaturemust be adjusted..TT-609 F TECHTIP Soldering Techniques Techniques StrainGageSoldering fiTRODUCTION The mostcommonmethodof makingelecaicalcontrectionsin strain gagecircuits is by meansof soft solders. Micro-Measurements soldering units incorPorateall of the abovefeaturesand a numberofothers' designedto helPthe user easily make consistent. the temPerature controller should be carefully designedto ensurethat it does not generateelecfical noise that could adverselyaffect nearbymeasuringinstrumentswhen both are in use. or even the test specimen. (919)365-3800 Telex802-502 FAX(919)365-3945 Group. methodsare basedon the use of a profesexperience-proven sionalquatity sotderingstation. Pointed tiPs shouldnotbe used.Bor27777 USA NorthCarolina27611. or screwdriver tyPe.and precision of soldering. An unregulated MEASUREMEI{TS GROUP to the power line. ln conffast.in conjunctionwith Microaccessories. The soldering tip itself should be of the flat.reliable solderjoints. In addition' the unnecessarily high temperahrrernay damage the strain gage. This tends to oxidize the tip.compression epoxies.These chamcteristicscontribute to the comfort.readily advantages to Providea rangeof. GROURINO.arealsoavailbonding.the solderingstation should incorporateprovision for adjusting the soldering tempemture to suit varying installation conditions and requircments. This is easily accomplishedby wrapPingone to two n(25 to 50 nm) of solderwire aroundthe working portion of the tip while the soldering iron is cold.a mixture is produced. and apply power to the unit.or with Micro-MeasurementsModel STC-I Soldering Tip Cleaner.or high-temPerature solder. it has a sharply defined melting temPeraturea characteristicthat largely elimirates "cold" solder joints. A liquid activatit maybe necessary for this ed-rosinflux suchas M-Flux AR is recommended purpose. both of which tend to impede the solderingprocess.SPeciallydesignedsoldering tips are recommended for high-temperature use.and D-alloy (modified Karma and IsoElastic) sfain gages. Techniquesfor rnaking leadwirecon[ections with silver solderaredescribedin MeasurementsGroupTeehTip TT-602' Stlver Soldering Techniquefor Anachment of I'eads to Strain Gases. and then the leadwirejoint can be completed using the same solder and M-Flux AR rosin flux or a rosin-coredsolder PREPARATION OF THE SOLDERING TIP New soldering tips should always be tinned with solder pdor to initial use. Wipe the excesssolderfrom the tinned tip with a dry gauze sponge.or test material due to overheating. This makessolderingmuch more conYenient. a liquid acid flux (M-FIux SS) is recornmended. NOTE: Cross-alloyingof solders car change the electdcal. temperature higher With usuallysufficient. l. -2- 2. Set the soldering station to the aPpropriatetemperahre rangefor the solder in use. solders.If rosin-coresolderis used. Silver solder (M-M Type 1240-FPA)is availablefor applications where leadwire connectionswill be exposedto temperatures above about +550"F (+290"C).it is recommendedthat only one type of solderbe usedwith each solderingtip. The te[dency for oxidation can be minimized by ensuring that excessmelted solder remains on the tiP at all times when it is not actually in use. and is padicularly useful in field applicationswherc accessory liquid rosin flux (M-Flux AR) may not be available. Acid fluxes should neverbe usedon constantanshain gagesor copper terminals. For routine applications. Never knock the heated soldedng Pencil against any object to remove excesssolder.termimls. or DCP) solder tabs of Micro-MeasurementsK. Of coMse. For making andto preventfurtheroxidationduringsoldering. The addition of a trace of antimony Provides superior performancewhen the solderedconaectionswill be exposedto very low (cryogenic) tempemtures for lollg Periods of time. containing chlorides. the following procedureis effecrivefor cleaningand re-tinning.with extemally applied acid flux (M-Flux SS)' is recommended for rnaking soldered connections to MicroMeasurements K. These solde$ are somewhat more difficult to handle becausethe higher working temPeraturerapidly vaPorizes the flux.After the tinning oPeration.Rosin-coresoldersshould rot be usedin coljunction with acid flux. In contast. thermal and rnechanicalProPertiesof the solderbeing used To Preventcross-alloying. SOLDERINGFLUX The functionof a solderingflux is to removeoxidationfrom the membersbeingjoined (soldertabs. bonding adhesive.or clean with the Model STC-l SolderingTip Cleaner. and Paste fluxes. While solders are sometimes selected to provide specific electrical or mechanicalproperties.With solid-wire solder. should not be used under any circumstancesfor strain gage soldering.no external flux is required.If the tip does becomeoxidized. Placeseveraldropsof M-Flux SS on a glassPlate. The general-purpose solders are supplied with a core of activatedrosin flux.and D-alloy strain gages.or wiping the hot tip with materialsthat char on the surface.or for splicing copPerleadltires. the most common basis for selection is simply the melting-temPerature range.will producea buildup of oxide that preventsProper soldering.however. to avoid damaging the gage. arl alloy with an intermediate melting temPeratureis the normal selection. The 63/37 tin-lead alloy (M-M Type 361A-20R) is an stain gagesoldering. are generally used for strain gage installaiions on nonmetalLic test Parts.leadwires). chemical. foil or leadwiresplices. wherc test condiiions do not dictate the use of either a low.Re-tin the solderingsurface by holding the heatedtip in the SS ilux while feedingsolderonto the tiP. Negligent rnaintenance pmctices. Solid-wire solder. and oxidizes the soldering tiP. When tinning bare (without soldering options S. This solder. as with WK-series gages using a special resistancesoldering unit. o . DC. This mixture cannotbe expectedto havem€lting and skengthProperties any better than those of the lower temperature component. Allow the soldering pencil to heat until the solder wrapped around the tip melts completely. in paste form.As excellentchoice for general-purPose a eutectic alloy.the wraPPed tip shouldbe dippedinto liquid rosin flux (M-Flux AR) to provide sufficientflux forinitiat tinning. before applying power to the solderingstation. Low'melting-point solders.or solderingdircctly to constantan solder is in a rosin-core contained copperterminals.SOLDERSELECTION The Micro-MeasurementsDivision stocks a broad range of soldertypes to meetvarious installaiionand testrequirements. A genercusamountofsolder is essentialfor propertinning' 3. to supplyadditionalflux. Remove excess melted solder ftom the tip with a dry gauze sponge. since this may result in personalinjury or damageto the solderingpencil. Setthe control on the soldering station to the apPropriatetemperature range for the solder. Oxidation of the solderingtip seriouslyhinders the soldering opemtion.if one type of solderis incorporated in a gage with solder dots and another type is added. high-temperaturesolders are normally selected testlng only when oecessaryto satisfy eleYated-temperature requirements. the residual flux must be comPletely neutralized within one to two minutes. is not suitable for anaching wires directly to strain gage solder tabs or to bondableterminals. for example.the flux however.but is intendedfor connecting instrument leads to preattachedstrain gage leads. The solderingtip shouldnever be fi. acceleratingthe oxidation and leadingto the early deterioradonof the tiP.the measuringgrid shouldbe Protectedwith SolderDots.andpressfirmly with the while tinnedhot solderingtip for aboutoneto two seconds.or solid-wiresolderwith M-Flux AR. with the flat surfaceofthe tip parallelto thesoldertabor terminal.sincethis may remove the plating on the tip.Place the solderwirc flat orl the gagetab. The bareleadwireendscan thenbe tinnedeasilywith thefoUowingprocedure: 1.Whensolderingdirecdyto bareKarmaor IsoElasticfoil.i For severelyoxidized tips.thenfirmly anchoredto thetest-partsurfacewith drafting tape before making the solderedconnection. Thenmeltfteshsolderon thehot tip to form a hemisphereof moltensolderabouttwice the diameterof the wire to be tinned.it is not necessaryto removethe residualsolderingflux at this time. it may be convenieotto use instrumentation stranded theterminaland a singlestrandof thewireasajumperbetween the straingagesoldertab. Fig.Gage griil and upper portion of solder tabs maskeilwith drafthrg npe. PDT-I &afting tape. NOTE: Specialproceduresfor tinning andwiring strain gages solderdotsare describedin suppliedwith preattached Tip TT'606.applyM-Flux AR to the wire end before staningto tin. If theM-Flux AR or a rosin-coresolderis usedin thetinning. for straingagetabsandterminalsconThe tinningprocedure and a smallamountofsolderto sistsof firstcleaning reapplying thehot solderingimn tip. areashouldbe alonga minimum Routinginto theconnection (such directionin a uniaxial as the "Poisson" stain directior . NOTE: Lifting the solderingiron beforelifting the soldermay rcsultin theendof thesolderwire becomingattached to the tab.roperUse of Bontlable Applications. This procedureassuresthatthereis sufficientsolder lift boththesolandflux for effectivetinning.theends tions or large-strainmeasurement. With solid-wire solder. smoothlytinnedateaon the gagetab or terminal. Soldering Tech Group (unencapsulated) Measurements open-face the solder tabs on tinning Before TechnQues for LeadAttochmentto Strain Gageswith strain gages. usinga dry gauzespongeor the Model STC-I SolderingTip Cleaner. Thisnot only shieldsthe grid TINNING AND ATTACHING LEADWIRES from solderingflux and inadvertentsoldersplash.led or sanded.the acidicflux residuemust b€ rcmovedimmediatelyfollowing the tinning operation. andProceedin the samemanner. andthis shouldbe donewith a thermalwirc stripperto the leadwiresizein use. lifting themin the reverseorder can leave a jagged (spike)solderdei:osit on the tab. -j- ernployingboadableterrninalstripsand For applications wire.using rosin-coresolder.This will producea smooth. it may be necessaryto repeatthis operationseveraltimesto obtaina properlytinnedsurface. TINNING SOLDER TABS AND BOI\. Leadwiresshouldbe formedandroutedto the straingageor terminalstrip. and washthe areawith a soft brush. However.DA3LE TERMINALS All strain gage soldertabs.of course. After the cleaning operation.In suchcases.applya droPof M-FluxAR to thetab or terminal(this stepcanbe omittedif a rosin-coresolder is used).applyM-PrepConditionerA liberally.The latter considerationis particularly avoid the damageto the wire that often occurswhenmechaniimportantwhenmakinggageinstallationsfor dynamicapplica' cal wire strippersareused.thenblot dry with a cleangauze sponge.Simultaneously deringpencil andsolderwire from thetabarea. of strandedconductorsshouldbe twistedtightly togetherbeforc tinning. When the operation is performed ProPerly. The of solder on the flow restricts Leadwireendsmustbe strippedof insulation.Hold thesolderingpencilin a nearlyhorizontalposition(<30').thesinglewire strand shouldbe separaledout beforetwisting and tinning the reGroupTechTip TT-603. andblot dry with a cleangauzesPotrge.re-tin andcleanthetip several times. 2.slowly draw the bare wirc addingfresh though themoltensolderwhile continuously solder to the interfaceof the wire and solderingtiP.terminals.After thewiresarestripped. If rosin-coresolderis used. Next.when M-Flux SS is employedto tin the bare soldertabsof K. useM-Flux SSon thegagetabsonly.Tinning strandedleadwircsto Producea formablesolid conductorwill alsogreatlysimplify theleadwAe attachmentprocedure. addingapproximately\18 in (3 nm) of freshsolderat theedge of the tip. Attempting to roue the leadwiresafter completingthe solder joint will often resultin damageto the gageor terminals.but also the tinned arca on the tabs.asshownin Fig.before soldertabsshouldbe only largeenoughto easilyaccommodate tinning.To removetheresidue. 1.it will Producea small.remoyeexcesssolder.shinycoatingof solderoverthebarcwire.and leadwiresmust be This helPs properlytinnedbeforemakingsolderedconnections. mainingstrands(seeMeasurements Terminals in Stain Gage The P.or D-alloy gages. ensureactivesurfacewetting andgoodheattransferduringthe solderingoperation.The clraftingtapeis Micro-Measurements positionedto coverthe entiregrid andthe upperPortionof the soldertabs. Removeexcesssolderftom the solderingtip. wash again with fteely applied M-Prep Neuaalizer 5A. 1 .Next. Thoroughly clean the entire installation area with generouslyappliedrosin solventand a soft-bristledbrush.Figurc 2 illustratesthis stagein the procedure.but they are most effective when used with professionalsoldering equipment which is specially designedfor making soldered connectionsin stain gagecircuits. because this may result in damageto the solderedconnectionsor the -strain gage grid.The equipmentshould not generateelectrical interferencethat could affect sensitivemeasuringinstrumentation.These practicesfrequently causelifting or tearing of the solder tab from the gagebacking material. If needed.with nojagged or irregularedges' and all tracesofresidual flux must be thoroughlyremovedprior to the application of protective coating.it is imPerativethat all traces of residual flux be completely removed with --.bend the leadwte end slightly to form a sprirg-like loop.terminal. stressfield) paniculartly for high elongationor dynamic tests' The tinned leadwire end should be fimmed short enough so that it will not protrudetbrcughthe connectionarea. and tapethe wire firmly -in place over the connectionarea.Do rot try to pull away the tape with tweezersor other tools. Solderedjoints should not be testedby pulling on the leadwire.using additionalflux and. without any Peaksor jagged areas. If the solderjoints are not smooth and uniform in size. will result in consistentlyproper and reliable soldered connections.In the final prepamtorystep. 3 -.'t4-t1MERosin Solvent.Any tracesof residualflux can causegage instability ard drift.This condi tion usually results from residualsolderingflux.permitting its easyremoval.The solderingpencil should be lightweight.and uniform in appearance.andflux removed. bondableterminals. Solderedjoints should alwaysbe smoothand shiny. using PDT-1 drafting taPe.with careful attention to detail.and leadwire ends should be tinned before soldedtrg the joints.Low or marginal resistancereadingssuggesta leakagePath between the solderedconnectionsand the test-partsurface. or by probing at the joint area. or from bare leadwte cooducto$ partially shortilg the gage tabs or terldnals to the test part. CLEANUPAND INSPECTIONOF SOLDEREDJOINTS After completing the solderingoperation.Solder selectionis basedPrimarily on the exPected operatingtemperaturerangeof the straingageinstallation:and all solder tabs. Residualflux mixed with a protectivecoating applica: tion can completelydestroythe coatingobjective.or bonding adhesive. If the iron -temperature is either too low or too high. . holding the solderingpencil nearly horizontal.shiny. it may causepoor solder connections. Printedin USA .and cannot -inadvertently make electricalcontactwith the test-pansurface or adjacentsolder connections. additional flux can be provided during the joiring operation -by feeding a little fresh solder into the joint from a spool of rosin-core solder This procedureshould result in a smooth.hemisphericalsolderjoint. Solder connectionsshould be Any solderedjoints smooth.Fig. SUMMARY The ability to make consistentlygood solderedjoints is essential for prccision strain gage measurements. Check the resistanceto ground of the comPletedgageinstallation.then lift the tip from the solderedjoint. and it shouldbe connectedto the solderingstationwith a very flexible power cord. and blot the area dry with a clean gauze sponge. using the Model 1300 Gage InstallationTester. Rcquirementstbr the solderingstationinclude low-voltageoperationof the solderingPencil.Apply a small amountof M-Flux AR to the joint area and.or it may damagethe stain gage.as shown in Fig. Clean and re-tir the soldering iron tip with fresh solder.Incompletelyremoved solderingflux is the most end taPed to surface in preparation commoncauseof degradedperformancein strain gageinstallations. firrnly press the flat surface of the tip on the junctiol for about one second.The samesolvent is usedto soften the mastic of the drafting tape. 3. that look questionableshouldbe re-soldered.andprovision for temperatureadjustmentto suit the tyPe of solder and the application conditions.The temperaturcof the iron should be adjustedso that the solderis easily melted. Use of the recommended materials and techniques. Visually inspectthe solderedjointsfor any gritty orjaggedjoint surfaces./orsolder as necessary. with a flat chisel or screwdriver tiP. without rapidly vaporizing the flux.and for tracesof flux. repeat -the solderingprocedure. The tape should be within abour ll8 it (i mm) from the connectionarsa. Cleanthe solderconnectionareauntil no visible signsof resid-ual flux remain. and will inhibit bonding of the installation'sprotective coating.The techniques describedhere are straightforward and easily mastered.I*adwire for sodering. Reference 6 . Actdand/ or cbloridetypefluxes.Thclong skaod can thctr br uscda! thc juEper wirc. andare bestfor generalu.Inc.4 it is oftedcorv€deut to cutall ltratrdsbllt ou.sin GROUP. Otherwise.lcaviogrcst 'doDe'of soldcr ---:-- +_ -1 11 1g-a. and allows the samesolder massto join both s€tsof wires.INC. This reducesthe bonded length of the terminals.O. Printcd-chcuit terminal strips are usually bondedto the specineawith th€ sameadhesiveusedto install the gage.USA (919)36s-3800 Teler 802-502 FAX(91e)365. l. orieat the long dimcnsion of the copperterminal along the sxis of minimum strain.3945 o Copyright Measuremenls Group.particulady the pastet]?e.The following instruotionswill assistgreatly irr sheining plspg1 performancefrom bondableterminals.Ilowever.In order to obtain maximum benefitfrom the use of theseterminals. and the fiberglass-epoxy termiaals (prefix CEG) are thcrefore preferredfor cryogenicapplications. 1 - Eal!-taminal' teclmiqn tor using bondetl termiuls in hish str.'The polyimide-type terminals (prefix CPF) have the bighestconformability and higbesttemperaturecapability. cousidcrably Orcstarnd .. Soldcriagis oade casi€rby this Ecthod.NorlhCaroline27611.03mm) electrolyticcopperfoil bonded to a carrier of either polyimide fiIm or fiberglassrcinforccd cpoxy.The prirnary purpose is to provide an anchor for both sets of leads.ranove all ffur rcsiduc $ter nldedng. Elecholyticcopperfoilbas aaiaherentlypoorfatiguelife. to fit thesiz.1983 All FlighlsRoseryed. 5.0014it (0.the terminal strip and jurnper wires should be costed vith a protcctive compound suitablefor the eavironmeat.TT-603 Bondable Terminals TECHTIP TheProperUseof BondableTerminals in StrainGageApplications It hasbecoae comnlonpracticeto employbondableprhtedcircuit terninals betweenthe main leadwire and the relatively small ard delicatejumperwiresto the strain gage. . Whenever possible. After solderi:rgand flux removal. the highexpansion coefficient of unfilled polyimide may causeloss of boad below -l00oF (-75oC). 2. of thecoppc!pad. BONDABLE TERJ\{INAL PATTERNS TTTTTTTT StyleC' StyleD' 3. 4.ds"ile is strand. and if the terminal irstallation mwt havc a long life under cyclic loading. l-l Stylc'C'terEiaal cut io half ledgth- Ti! cltit€ qoppcr pad.'-r-i-. Micro-Measurcmentsorinted-circuit t€rminals are produced ftom 0. MEASUREMENTS P.se.the termilal can be a sourceof performancedegradationfor tbe cntire installation.-. Failure of tle copper betweensolderjoints is prevented by this techdque.andselectterninal sr?e appropriate to the AWG size of the main leadwires. maycausethecopperto unbotrdfrom StyleT. aad.they must be installcd with care aad knowledgeof their limitations. Selecttermiral corrfigwstion to match the geometrioal arangemcnt of the gage/lcadwiresystem.g€nerallyth€ same compoundusedover the gageitself. If the strain level exceedsi500p€.rng guatos oelorc solderilgto tarEioal Fig. Useonly rosh-type solderingfluxes(suchasM-Flux AR) on prioted-circuit terminds.Eor277n Ralelgh. aud to prevent forces transmitted along the main leadwiresystemftom damagingtbe strain gageor degrading its performance. l.. Micro-Measurementsmanufacturtsboth typesia a wide varietyofcotrfigurationsasdescribcdin M-lV CatalogA-1I0.' MEASUREMET{TS GROUP rr tt ll TI TT TI Style'S' wlle NOTE:Whenthc oaiq L. usethe 'C'codiguration termiualscut in hslf asshownin Fig. 4. and bondilg failure will occur at the locatiotr shown. snd deot oll tape ruidae and flut with rosin solvent 7. No tc. Useneatsolderjoitts ot all t€rminalswith the same amount of solder qn each. 10. andthen solder tbe wirc to tle pdnted-circuit ternhd usingrosin flux. aad often deate seriouselectricalleakage problems. thcr all thlcc l€adr alc tlioacd ald soldelcd diftctly to lhe coppcrcoatcd tabs. 002621GP SidcVicw Useof SEl.MeasurementsGroup TechNote TN-501providesa detailed discussionof aoisecontrol ia strain gagcmeasurements. particularly whenhigh heating or cooling rates are iavolved.Na owpiece o! MlIu tqe or fudting trye used to preeent excets qrcad oJsoklet Removetrye alter sol' dairy.aad stressreliefloops maybe undesirableia thesecases. The Type 'S'terminal.Dgthereal symmetry.R.thcr. Ofteu uacd wheagageshaveirtegraljumpe!lead5.If the termindl backiag is placedagaiostthe gagebacki"g i:r aa M-Boad 200installation.si* 'C' tcraioals caa be NOTE: Thc abovc Eethodr usitg Stylc 'half-tcleia8l'tcchriquc sboptr itr Fi8.renove flux rxidue.a "stressrelief loope is usedin the jumper wires between terrni-nalstrip and gageto mini i"e forcesappted to the gagetabs. 2 .UseolStyle'S'terninal to make a three-wbe csble connection.efetlo MeasurementsGrot4tTech Tip TT-601relaling to tecbniquesfor bonding leadwires to surfacesexperiensinghigh centrifugalforces. Fig.the backing.5 mm) awayfrom the endofthe gagebackingto avoidunbording problemsdue to thick areas of adhesive. pre-tin the wire with an active acid flux such asM-Flul SS. When priatedcircuit terBinds must be usedi! this type of applicatioD. When terminal stripsareuscdwith high-elonption straia it is Prefenbleto locate gages(post-yieldmeasurements). Printedln USA . The "hall-terminal" techaique@aragraph4) is usually employed ia high+tougation work if the strai.Exaggeratedsfule sbip too closeto gtga Excesshte lation with tenninal adhesivebaikls ap at bottom ol ga$' andlotms a Jaihre point tader high tuatn condit'ans 8. a "ramp effect' results as shown in Fig. This prevents nonuniform solderspread. Wheneverpossible.If tbe leadwire system is an alloy that must be solderedwith a corrosive flux. 3 Stylc'C' Terminals 2 Style 'C' Terminals Adh. 3. g.nlevel will exceed?lo3Vo. Figure 2 shows the useof a narrow pieceof Mylar tapeto maskthe center area of a set of termiaals.nal strip at ]f. with thc coabiacd 'Ycrtical'strcss-relicf loop. viewol M'Bond200 hstal' Fig. or in a perpe.3 .Thefigures ia this Tech Tip show various methodsof terminal use in gagecircuits. especiallyat elevatedtemperature. 1.l . has a u:rique construction. Addltional Wire Configuretions various Eethods of Eakilg three-wile cable couDcctioDs. Note that in every case.locate the termiral stdp sothat the centrifugal force is either parallel to the planeofthe terminal.This arrangem€atis popular where soldering and desoideringof leadwires 'S' may be €ncountered. 'L' tcrmhd to brin! Eain lcad cablcoff at right-anglerto gag€axis. Theseproblemsare miniarizedby keeping thermal massesatrdjumper wires assymnetrical aspossible. Thermal EMf generationand leadwiretemperaturedifferencescatr createsignificanterror siglals in strain gage circuits.andassistsin obtairi. shown in Fig. Please note that redustion of electromagaeticnoise pickup requires special leadwire considerations.ut | | 16n (1.Type terminals ars not recommendedwherehigh cyclic cuduranccis required. the terDi.Twoof thc lcadwirEs 8tr t{iltCd tc.and to preventwire failue at the solderjoints. the hole in the centerprovidcsthermatisolatioi betweenthe solderingareas. Fig.and kcep alljumper wires the samelergth from termhal stdp to g€e. kcepthe solderand lsadn'irs pas5 1s a minimum.ndiculardirgction qhirchwill assistin kgepin_g the terminal iu place.Dinals arc rcqutcd viih a CEAtypcgagc. Terminal Bo!d failure Pout 9. High g-fields createbigh unbonding forccs betwcenthe copper termiral and backing material. 7 Reference . mount of uubalaice' GROUP.and stain ilto measured errors wire syst€mwill introduce stain.d.t the bridge is resistivelysym. varying gage To circuit.thewiriag schemechoseato comectthestain gageto tbe bridge circuit has a sigoificanteffect on the accuracyof stmindata' measured In particular.a differential voltagewill be preseatat the outputcomersof tbebridge.1996 All RlghtsBeserved.Itr this condition. If the bridgeis not in balance.2) produce a zerd output voltage when the test Part is at rcst.arc connectedindePendently in the foliowing discussed As arrangemenl ir a quarter-bridge sections. and resistance of temperature-iDduced 3) orovidefor compeasation eachof degees.ry ago.the bridgeis saidto be rEsisdvely bakn.temPeratule clata.Box27177 Raleigh.I - Bridge CbcuiL BasicWheatstone 'W}ile a mathematicalproof is beyondthe scopeof this Tecb arechosensuch it car be shownt!'at if the armresistances Tip.trtial outputvoltage(er) is measuredat the ts'o remaining bridgecorners.O. configuration.R ' connectedin a series-parallelaraqgement. The electical conaections$'herePails of bridg-earmsarejoined to theleadwiresftom theexcitationvoltageiource arereferredto ashPut comersof tbe bridge'A diffe.or bridgearms(Rl' R2'R3.theWleatstonebddgehasbecomethe sensingcircuit of choicein mostcommerciallyavailablestrain This PoPuladtyis duein largemeasueto saseinstrumentation.TECHTIP TT-612 0uarter-Bridge Gircuit Circuit Quarter-Bridge TheThree-Wire TIIE WMATSTOI\IE BRIDGE INTRODUCTION straingagemore Sincetheinventionof the electricalresistance tbana half c€lfi.INC.andreduces contbee-wire the Consequendy.. w M EASUREMENTS GROUP V bridgecircuit in its simplestform €ig' 1) conTheWheatstone sistsof four rcsistiveelements.ficantresistance in theleadchanges offsetin thestlai! gag€circuit.USA (sr9)365-3800 FAX(919)36s-3945 ooopyrightMeasurem€nb Group.Inc.whetherftoE uniaxialor rosettesEaingageconfigubridge to theWheatstone rations.useof a two-wirecoonectiotris generallynot recommendedbecauseit may introducea signi. saain tne ir cianges thesJfactorsis essentialfor accuatestain g€e measurcments' In themajority of stlain gageapplicationsfor tbe determination of thestaieof stresson a test-pafisurfacqindiTidualstain g€e elements.referredto asoutputor signalcomers' Fig. MEASUREMENTS P.metricat lirc drawntbroughtheb'ridgeouput comers(asis thecasewith mostcommerciallyavailablestain gageinstumentationandas assuraedin this Techlip) the differential ouFut voltage(er) of the valueof theexcitation will be ideuticallyzeroregardiess suDDlvvoltage.NorthCarolina27611. the two-wire saain quarter-bridge for hookup the recormended is nection gagecircuitsfor staticstain measuleoent. procbanges detectthesmallrcsistance to 1) ability its-inberent dimenminute even gage it follows when sfiain in the duced sionalchangeson the surfaceof a testPartunderload. aboutan imaginary th. .gege the of tbe sensitivity will reduce theleadwiresystem ctcui| Configutingthe stail gageinput asa thrce-wirccircuit providesfor intrinsic 'bridge balance"andautomaticcomPen' on meaiation for the effece of leadwketemperaturcchanges in sensitivity the loss Prcsenti!' sw€d strai! data.and the magninrdeof this outPutYohsgewill be proportionalto the g.and an excitation voltaqesource(F). TEREE-WIRE CIRCUTT TWO.WIRE CIRCUTT For aa initially balanced bridge, if one of the bridge arms is replaced with a strain gage of precisely the same resistance value aud coljlected with two leadwires having negligible resistance, the bridge remains at balance But in practice the leadwires will have some measurableresistance (R/ as shown in Fig. 2, which may re.sultiu a signiflcant lack of syDmetry in the bridge. This occurs becauseboth leadwires are in serieswith the saain gage between, for examPle,the posilive (+) inPut comer and the negative (-) output comer, adding to the gagearmresistance. That is, the gage ann resistancebecomesRc + zRr. Thepreferredcircuit for usewith a singlestais gagein a quarter-bridge configuration is the three-wire circuit shown in Fig. 3. Itr the two-win circuit, both leadwiresarein serieswith the strain gagein one arm of the Wheatstonebridge. In the three-wirecircuit, the fust leadwirercmainsin serieswitb tbe strain gage,but the secoqdleadwire is now in series with duEmy resistor& betweetrthe negativeinPutandouq)utcornersof thebridge.Referringto Fig. 3,if thosstwo leadwircsare the sanetypeandlengthandexposedto the sametemPerature, fl.et rcsislances wiU be equal.The two respectivebddgs arEs the bridgeis againresiswill thereforebe equalin resistance, tively symmetricalabouta horizonal line throughtbe bridge outp[t comem,and the bridgeremainsbalancedregardlessof leadwiretemperatulechanges,soloog asthe two leadwiresare And becauseonly oneleadat tle samelospectiyetemperature. is wire is in serieswith thestraingage,leadwiredesensitization reducedabout50% comparedto the two-wie configuration. wire only andit is The third wire in Fig. 3 is a voltage-sensiag not in serieswith any of thebridgearms,thereforeit doesnot affectbridgebalanceor temperahfestability. Fig. 2 - Two-wirequafter-bridgecircuit. As a measue of the magnitudeof this effect, considera 120ohm sftain gageinstalledat a distatrceof 20 ft (6 tn) ftom tlj1e iNtrumetrt, and coqnectedto the illstrumeD.twith a Pair of AWG26(0.4 mtndia")copperleadwires.At room temperatue, the total resistancein serieswith the straia gageis about1.7 ohEs. For atr instrumeDtgagefactor setting of 2.0, this proto ducesan initial imbalancein the bddge correspotrditrg approximately7000pe. Further,the leadwiresare a pamsitic in the gagearm of tbe bridgeandefectively reduce resistance or desensitizethe gagefactor of the saain gage,resultingin a reducedsignal output wheu the test part is subjectedto test tle percetrtage loads.For Eodestvaluesof leadwireresistance, of lossin signalis approximatelyequalto the ratio of leadwire I.trthe examPlegivenhere, resistasceto stain gageresistance. tlis resultsir abouta 1.570lossi! se$itivity. Theinitial imbalancemaybe offsetusitrga strainindicatortbat subhasa sufEcientbalancerauge,or maybe (mathematically) stain readings.However,a moreserious tsactedftom mea.suled problemmay resultif thetemperatueof tbeleadwireschanges duringthe meas[rementprocess,causinga coEesPondil.g leadwircs CoPPer cbargein resistanceof the interconaecting 22Voof.their approximately itr resistance leadwireschange resistancevaluefor a 100"F(55'C) temperaroom-teEperature tue change.For the 120-ohmgagecircuit above,this would resultin anerrorequivalentto apFoximately156/r€for a 10"F (5.5'CJtempentue changein theleadwiresystem. The erors and problemsspecificallycausedby the two-wire circuit are dueto lhe pair of leadwiresin serieswith the strain gage.Al1 threeof tbeeffectsdiscussed hereinffeasein sevedty with increasedleadwire resistanceiand the two-wirc circuit offersno intrinsic compemation.It is wortbnotingthatuseof a 350-ohmstrafugagecircuit will reduceeachof theseeffects, but cannoteliminate completelythe associatedmeasurement enors.But a straighforwardmethodexiststo reducethelossi! sensitivity,andessetrtiallyeliminaietheiDidaiimbalaaceproblem and the 6rror that resultsftom tempemturechangesin the leadwiresystem.This methodinvolvessimFly addinga third leadwte to theshaingagecircuit asshownin Fig. 3. September, 1996 E2,t-+ Fig. i - a+ e6. Three-wite quarter-bridge circuit. over the While the tbree-wirecircuit offe$ seveEladvantages two-wte circuit, in somespecialapplicationsinvolving, for connectors, not enoughconexample,slip ringsor feed-tbrough nectionsmay be availablefor a continuousthree-wiresystem from the gagesite to th€ instruEenttefidnals. In thesecases, useof a two-wireleadsystembetweenthe straingageandthe connector.anda three-wirecircuit betweenthe connectorand to minimizethetotal themeasuringinstrumetrtis rccommeuded lengt! of thetwo-wiresystem. The foregoitrgdiscussionappliesprimarily to mea$rementof static stains with a measuringinstrumentthat proYidesdccouplingbetweenthe bridgecircuit andthe amplifierinput terof purelydlnanic strainswhenonly minals.For measurement amplitudeof a time-varyiagstrainsignalis of thepeak-to-peak be usedeffectiveinterest,thetwo-whesystemmaysometimes amPlifierthatprovidesfor ly by selectinga sigual-conditioning ' ac-couplingof the input signal,to "block the effectsof temperature-ilducedchangesin leadwkeresistanceon the strain slgDal. In sunmary,benefitsof the tbree-wirecircuit includeinainsic bridgebalance,automaticcompeNationfor theeffectsof leadwire temperahrrechangeson bridge balance,and increased sensitivitycomparedto the two-wirc corfigurameasurement conEguration tion. Thetbree-wirehookupis therecommended for quafier-bridgestain gagecircuitsfor staticstrainmeasulement.The two-wte circuit can sometimesbe usedeffectively with for specialsituationssuchasdynamic-onlymeasurements ac-coupledinsuumentation,or in stati.cstlai! apPlicatiotrs wherethelengthof thetwo-wiresystemcanbekeptvery short. Printedin USAby GP 8 Reference Micro-Measurements Strain Gage Accessories M-Coat A Ilescriplio* Air-dryihg solvent-thinned(xylene)polyurethane.Transparent.Moderatehardness; eoodflexi:biliw.Canbe removedwilthM-LINE RqsinSblvenror toluene.Fi.lm coatingfor lab in (0.10-0.25mm) per coat.General-purpose ihickness0.005-0.010 additionof cured before fully Must be field applieations. base coating for use,andas by many solvents. attacked Not readily moisture resisiance. coatings. Good other Convenientto use. M-CoatA Kit Csre ldequirements Dries tack-heeat room temperatuein 20 minutes.Completelydry in 2 hours.Normal cure24 hoursat room temperatwe.Chemicalresistanceandcoatinghardnessincrease for6toTdays, R.ange OperatingTen:perature ShortTerm:-100"to +300'FC75'to +150"C) I-ongTerm:-100"to +250"F (-75"to +120'C) Shell Lif'e* I yeatat+75"F (+24"C) Ordering infbnnation o M-Coat A Kit (asshownabove)4 brush-cap bottles[1 oz (30 ml) ea] PROCEDTJRES L Leailwire Preparation and Priming Step 1 Using brush provided. It may be desimble to thin the M-Coat B by mixing it 50:50 with methyl ethyl ketone (MEK). and M-Coat B (an air-drying dtrile rubb€! coating). consult the materiai safety data sheet. Step 3 Cut a patch of M-Coat FB butyl rubber sealant large enoughto eKterldll2 in (13 no ) beyond the three open sides of the gage (or Teflon filn). All kit components have flash points above +llQ'F (+45"C). heat lamp.Q. These matedals can be aPPlied to vertical aad inverted surfaces without flowirg. On encapsulated gages. HANDLING PRECAUTIONS All components of the M-Coat F Kit arc safe to use when reasouablecare is observed. The qormal operating temperahue range of M-Coat F is -20" to +175"F (-i0' to +80'Cr. and pressue vessels.petroleum products. prime viayl-insulated leadwires with a layer of M-Coat B and allow to air dry. for best rcsults.110. Application of M-Coat F consists of pressing a small piece of Teflon filco onto tl€ exposed gage foil and lead connections. motor vehicles. only the solder connectioas need be covered. IL Application of M-Coat FT T€flon Film.Instructions FApplication M-Coat INSTALLATION INTRODUCTION The M-Coat F Protective Coating Kit is desigftd to fit a wide vaxiefy of both bondable and weldable strain gage aPplicatiot rcquirements.tnc. On open-faced gages this would irclude all foil areas and solder contrections. Step 3 Attach the leadwires and remove all soldering fluxes according to recommended procedures for the materials used. 'Contents includi sef-adhering Teflon@ film. Shelf life is one year. For mechanical Protection. Pliable butyl rubber sealant. Aaleigh. Strippiog and tindng after priming or etching prevents the pdmer/etchatrt from touching bare conductors.irect contect with M-Coat B: (2) Avoid prolonged or repeated breathing of its vapors. it is particularly suited for use where working conditions are not ideal. reinforcement ba$ itr concrete. and FN Neoprene Rubber Step I Clear the gage installation area with a suitable degreasing agent to ensure a tenacious bond of the coating.USA P. tutrne1s. @Rcgist€ledTradema* of DuPolL Division Micro-Measurements GROUP. protect and waterproof the splice joiots with a heat-shrinkablesealant(M-M rrsT-1). Obtain medical attention in cases of ingestion or extleme exposure. Fts Butyl Rubber..bddges. Pressin place.aluminum foil tape. This kit contains all materials necessaryfor instaltrationunder general laboratory conditions or in hostil-efield etrvircnments. For additional heaith and safety information.1994 .Box27T/7. BecauseM-Coat F is easily applied ard requires no mixing or curing. but may result in softening or reduction in bond stength. or flowing air or water. and at least 1-114ia (30 mm) beyord tlle end Telephone(919)365-3800 FAX(919)365-394s Printedin USAby PP August.INC. warm with a heat gun. @Copyright Measurements Group. aircraft. Cleaned area should be slightly larger tban the space to be coYeredwifh M-Coat F. FA aluminum tape is installed over the etrtire installatioa and sealed with M-Coat B. ships.) NOTE: When splicing lengths of leadwire.Eoshould extend 1/16 in (1. If the surface of the specimen is betow +40'F (+5"CJ. Operation in an extendedmnge of -70' to +250"F (-55" to +120'C) w\llnot damagethe coating.1978 All RightsFleserved. etc.neoprenerubber sheets. a soft. Typical applications include pipelines. This forms a smooth contour and provides additional protection against moisture and solveots. IJ skiD contact with M-Coat B does occur. The fil. the user is cautioned to: (I) Avoid d. (Refer to M-LINE AccessoriesCatalog A. (3) Use M-Coat B only in well-ventilated. Etch uRtreatedTeflon-insulated leadwircs with a Teflotr etchant such as Micro-Measurements TEC-I TenaEtch compound. however.. Step2 Cut a piece of M-Coat FI Teflon fiLn large enough to cover all exposedelectrical surfaceson the gage installatiou. thoroughly flush the contaminated area with warm water. heavy machinery. Separatethe individual conductors of flat multi-conductor cables prior to priming or etching. a layer of M-Coat FN neopretrerubber is pressedorlto the layer of EB sealant. This is followed by a layer of M-Coat FB butyl rubber to immediately seal agaiast moistue.areas. MEASUREMENTS NC27611. In applications exposedto solYents. Step 2 Strip aod tin each teadwire.5 nm) beyordbarc foil and electrical comections. Leave I ia (25 mn) ot he sealantexPosedasshown. press this exposed area to the surface of the insta.For maximumstength.o. Step 4 Remove the protective paper from one side of the M-Coat FB patch.) M-CoatFA-2 . Step 7 Cut aluminum tape to a length at least 1 in (25 mtn) lotger than the installatio!. 3 NEOPRENE FUEBER Step7 M-CoatFA aluminumtapecanserveasa convenietrtleadwirc restraint. This is particularly imPortant with M-Bond 200 cyaroacrylateadhesive.2mm)ttuck M-CoatFA . 2b). M.NeoFen€RubberSh€ets 12 pcs.Coat F Installation with Aluminum Tape In applicationsexposedto solvetrts. installatiotrof alumi!.Air-Drying Nitrile RubberCoating four 1-oz(30-nl) btltsh-capbotdes . applicationof M-CoatB ssalsthe edges.003n (0. cut a patch of M-Coat FN neopreue rubber approximately ll4 in (6 mrn) smaller (on all sides) than the butyl rubber. PROTECTIVE PAPER SEALANTOVER EACHLEADWRE Step6 For mechanicalprotection. beginning at the end opPosite the leadwires and stopping 114it (6 mtn) past the solder connections.) M-CoatFN-2 . being carcful oot to puncture tie sealant (Fig.ButylRubbersealaat(25pcs.Butyl RubberSealant 12 pcs-3. raise each lead and tack to the coating.Removetheprotectivepaperftom the butyl rubber.NeoFeneRubberSheets(25pcs.(3.3.75 n (95 mn) sqtaft. Allow the frst coat to dry to the touch before applyi-ng the second. 3). Use a dental probe to form tbe sealaut arould each lead.Ai!-Dryitrg NitsileRubberCoathg two 0.5-oz(15-nIJbrush-capbottleJ BI]LK REORDERQUANTITMS Itr.1ustrates a completed installatioo. Step 1 through 5 Follow procedules in Steps 1 though 5 in Section II.lEin (3. the FN neoprene sheet can be eliminated ftom the assembly. Press the foil flrmly into place arcuud the iNtallatior aod leadwires. However. Fig.of the gage or termiml strip ftom which the leadwtes exil If the gage-bonding adhesive extends beyond this ares. 1.petroleumproducts. M-CoatFB-z. Request Bulletin 318 for d€tails' KIT CONTEI{TS M-CoatFT . 4.Sef-AdheringTeflouFilm x 0. Firmly press the remainder of the patch onto the specimensurface (Fig.08mtd tickx2'tt (50 twn)' idex 20 ft (6 n) loag M-CoatB .llation.are M-CoatEB.The aluminumtaPe contou$ the iustallationand leadwte routing.fold asshownin Fig. Step I Apply two coats of M-Coat B to the taPe edges. As shown in Fig. NOTE: wlen a 1ow-profile installation is desired.umtapeatrdsealing with M-CoatB offersincreasedprotection.003iu (408 rnrn)thick I pc. 0.125in. Figure 5 il.2 n)frrick M-CoatFN .paying particular attention to the lead exit area. This technique minirnizes the oiherwise steep edge over which the alumiaum tape is installed. Various installation techniques are described on professionally prepared videotapes available from the Measuremeuts Group.75in (95run) sqnede.andpressthe neoprenein place(Fig.AluminumFoil Tape. caution must be exercised with this method since it provides less mechaoicalprotection.cut a patchof M-CoatFN neoprenerubberto the samesizeas the butyl rubbersealatrt. Fig.4 in (100mn) squ. flowitrg wateror air. Step6 For mechanicalprotectiotr.zGft f6-tr) ro[ M-CoatB .AIuEiEumFoil Tape 0. and long enough to cover the desired length of leadwire. Smooth the tape edges with a bluot instrument. I Step 5 Usiag tweezers. increase the size of the patch accordingly. 2a). .'] I J 9 Reference .} I I i I J I I I l I I I I I -.I I I a I .. This Tech.Blot with gauzespongesandrinsewith water.andwhengagesarebondedto reiaforcementbars. Rinsethe areathoroughlywitb cleanwater. . abrading.itrcludingconcrete.measurementsgroup.For example. or on reinforcemetrtbaxswithin the saucture.Rinse with cleanwater.an exaa operatioamustbe addedto fill the voiclsand sealthe surfacewith a suitableprecoatingbeforethe gageis De$easing Usea stiff-bristledbrushatrdamild detergent(Fig.NorthCarolina27611.leadwire and protective coating selectionsand installations under these conditions.or grit blasterBlow or brushall loosedustftom the surface.GROUP V Fig.ditioner A.A n w M EASUREMENIS .Removesurfaceirregularitieswith thewirebrush. INSTALLING STRAIN GAGESON CONCRETT AND OTIIER IRREGIJLAR SURFACES SEaingagescan be satisfaclorilybondedto almostaDysolid matedal. to the surfacein andarouadthegagingarea.if tbesurfaceis properl.applicationof layout lines. a nildly acidicsoluGer:ercusly tion. .For smoothsurfacesou uotrporousmaterials.. whether measwementsatemadeon tle concretesurfaceor withir the condete. degreaser suchasCSM-1A may be neededif oils andgreases arepresent.USA (919)365€800 FAX(919)36s-3945 http://unw.For con$eteandothermaterialswith ah uneven.a discsander.com @Copyright Measurements Group. conditioningand leutralizing arerequired. provisions axenecessaryto protect the installationftom mechanicaldamageduring fabrication and from the hostile environmeDtof the concreteitself.Condilioningthe surfocefor gageinstallation MEASUREMENTS GROUEINC. Conditioning applyM-PrepCoD.Tip oErlinesrecommendalionsfor gage. M-LINE Strain GageAccesories.The surfacepreparationmaterialsand imtallation accessoriesreferencedthroughoutare describedin detail in Micro-Measurements Catalog L-110.Dry the surfacethoroughly.TT-611 TECHTIP D Concrete Structures for ConcreteStructures StrainGageInstallations INTRODUCTION The installatiotr of straitr gagesfor concretestnrcturespresents several unique challenges to the installer.Scrubwith a ConditioqerA with stiff-bristledbrush.A'.Blot contaminated gaue sponges.only the basicoleratiols of solventdegreasing. P.1 .Box27777 Raleigh.roughandporous surface. Reducethe surfaceacidity by scrubbingwith M-PrepNeutralizer 5.1995 All RightsRgsgrved.gage.Warmingthesurfacegendywith a propane torchor heatCunwill hastenevaporatioD.lnc. 1)to remove aay loosesoil or platrt growth.ypreparcd.special preparationis required to ensurethat strainson the irregularsurfaceof the concretearcful1y tratrsmitted to the strain.O. however Fhst.Nignment.Excessiveheating of the tabs can be elininated by using gages with Option W (itrte$al printed circuil terminal). Fig. or Option P (preattachedleadwires).which tend to lie flatter during haadling. the gage length of shai! gages used on conqete should be at treast5 times the diameter of the lagest aggregatein the concete. and level to form a smooth surface. M-Bond GA-61 is recommended. Scrub them with Conditioner A. contact our Apptcations Engineering Depaftnetrt for recommendations.Fining Application of a ioo%-solids adhesive to the gagiEg area @g. At higher temperatures. Supplementallayout lines may be drawu wi& ink otr the cotrfiete outside the gaging arca. Further. 3 . 6) are speciallydesignedfor measurement of mechanical strains within concretestructures. will be used to bond the gage. bonding with a quickcuriagadhesivel like M-Bond 200. In applying the adhesive as a soaler to the surface. which is shownin Fig. work the adhesiveinto any voicls. will allow time for realigni:rg the gage.5 .like M-Bond AE-10 shown in Figs.Series or encapsulatedEA-Series gages. Gage Bontling Normal plocedurcs should be followed for bonding the gage to the prepared gaging surface. 2) will provide a suitable gage-bondiag surface. M-Bond AE-10 is normally used. and dry asbefore. Special notice should be paid to several points.if necessary. are higbly recommendedfor their easeof installation under these circunstances. Accurate gage alignmeut ard an even appl. is not rccommended.andis firlly encapsulatdd -2- Fig.It will also enablethe use of a suitable pressurepad and clamping fixture as oudined in Measuements Group Tech-Tip TT-610. This often resultsin the use of panemswith gagelen gfts of L Ia (25 nltn) or more. 3 and 4.(If a thin adhssivs. After the adhesiveis cBTe4 it should be abradedwith 320-grit abrasivepaper untd the basenaterial is exposed. Fig. 2 .lhe seming grid has an stains in ag$eactiregagelengthof 4 it (100run) to ayel3:ge in a polymerconcrete gatematerials. even when test conditions may warrant its use. 5.A slower curing adhesive.4 . care should be taken when soldering leads dtectly to the stain gage.Adhesive qplication Soldering Coacrete and adhesivefillers are relatively poor heat conductors. bumish layout lires. Attention to theseprocedureswill help ensuresuccessfirlinstallations of strain gageson the surface of concreteatrd other similar solids. apply Neutralizer 5A.ication of pressure as the adhesive is cured are more dificult wheu booding longer gages. For test temperaturesup to +200"F (+95"C). Accordilgly.Finisheil installdion with MA-0640C8Y-120gage wilh OptionP (preanachedlzadwires).Fihing of the surface. If you have any questions about your particular applications. STRAIN MEASI]RAVIENT WITEIN CONCREIE STRUCTIJRXS Micro-MeasuementsEGP-SeriesEmbedmentStrain Gages (Fig. NzA. like l\4-Bond 200. the basematerial should not be exposed") Fig. Lsyout Lines Using a ballpoiut peu or rourd-pointed metal rod. . and to protect against moisture aod corlosiye attack. 7. CableSplices 9..D material to closely match the mechanical propertiss of typical sEuchual concrete.ciendy large descaledarca for gage and protective coating irstallatiors. 4.CEA. Strain gagei. STRAIN GAGE INSTALLAIION ON CONCRETEREIMORCEMENT n.ostallationon reinforcingrofu follows the same generalprocedurerecommended for moststeelspecimens. tie leadwirccableto any availablesupport. 7) maybe used. EGP-Series Gages incorporate a. -3- .6to 3. Degxease (150-mm)lengfhof fte bar at theproposedgagelocatiou. Surfacefinish shouldbe 63 to 125micrciach( 1. Wipe dry with gauze sponges. When conditionsare not WK-Seriesgagesare recommended. (Aluminum oxide or silicon carbide abrasiye of apprcxi. Theserodsare. Fig. GageSelection CEA-Seriesgagesarethe mostpopularchoicewhentbe cross sectionof ttrebar is Ll9ln (3tnm)or largerin diametelmere verystableirstallationsarcrequfted(e.) A3-in (75-mn) length generally provides a suffi.A aod a cottou applicator and wipe dry with a gauze sponge as previously ooted. Lay out the gage locations. guard against mechanical damage.9. GageInstallation No preparationof the gageitself is required. and are compatible with conventional stain measEementinstrumentatioE.CW-Series WeldableGage. 3.normalpouringtechniques requAed. EGP -Seies Embedment Gage. 2.Careshouldbe taken to andto tie seculethegagein thedesiredlocationandorientatioD.EGP-SeriesGagesmust be -bo. Scrub the area thorougbly with Neutrdlzer 5. Mask atr ar€a with PCI-2A cellophane (or MJG-2 Mylar@) tape at the gage location to minimize flow-out of adhesive for subsequentprctective coating alplication.nections with andthetrprotectedftom moistureaddothercontamination a suitablecablesplicesealant.p-d-s$arn. Wet abradewith Conditioner A aud 22Ggrit silicon carbide wet-or-dry paper (SCP-1). Descaleand smooth the rebar arouad its circumferencewith a grhder wheel. gages.andLWK-SeriesWeldable Gages(Fig. 6 - 8.uexcessof one year) ou 1/4 in (6 mm) or larger diameterrebarrod.thefollowing speamoist. ?.corosiveenrrircD-Eent cial anerrionis required: t1 SurfacePreparation with a degreaser(CSM-1A) over at least a 6-in 1. M-Bood 600/610.. shouldbe soldered Whensplicesarerequircd. jacketed. Wipe dry with a clean gauze sPonge (GSP-l). 5.howeve!aswith ge-!d. Other adhosives that may be used.re.mately50 mesh is preferred. depending upotr the test envtonmeot.subjectedto mecbanicalabrasionand Accordingly.for testsi. Use sufEcient Conditioaer A to prevetrt material from drying on the rebar surface while abrading. are M-Bond AE-15. l0-ft (j-m).2 W) rms at the completion of the secondwet-abrading operation.however.Application of the arlhesive should follow the specific insauctions &LvuP@JruE EGP-SeriesGagesare providedwith a 10-ft (3-n) cable to allow for makingcablesplicesoutsideihe concretestruch. This adhesivewill cure iu 6 hours at +75'F (+24"C).sdgd. or GA-61 adhesive. favorablefor bondinggages. 6. Scmb the iustallatioa area with Conditioner A aqd a cotton applicator (CSP-1). Surface finish after this operatioq should be about 180 microinches (5 W) tms. three-conductor cable for ease of use in field installatioDs. Adhesive Selection M-Bond An-i0 adhesiveis a good selection wh€o a roomtemperature cure of a field application is required.all coa. This step must be accomplished thoroughly to neutralize all toacesof Conditioner A used in Steps3 through 7. then rePeat Step 3 (wth 320-gnt paPer) aud dry again.pt direcaccuatelyalignedalongtheintendedshainmeasulemetrt tior during the imtallation process. Fig.befoletheconcrete is poured.While the EEb€dmentGagemustbe completely encapsulated in concreteto ensuecompletestlaiatransferfrom areusuallyall that are thestrucfirle. 361A-20R solder will give excellent results. M-Coat B. Fig. it is good practice to use a three-leadwte system. or +hows at +L25'F (+50'C). and should be carried back far enough to cover the leadwLe area previously primed with February1998 Cut-away view of installatinn.lowing the procedures oudined in Mcro-Measurements Itrstruction Bulletin B-14?.ires may be soldered to the shair gage tabs after gage bonding. Micro-Measuremetrts EA. thermally srip the leadwire ends and tin and solder the wires to the stain gage tabs. the instrumeutation leads extending from the gage. If a parailel or rwisted cable is used. For most lebar installations. A Foper$ installed aad protected shain gageis capableof maay yearsof service on embeddedreidorcing bars. Altematelt leadq. the complete installations should be thorougbly checked with a Model 1300 Gage hstallation Tester befole and after the concreteis poued. remove all losin flux ftom the soldercd connections usiag rosia solvent (RSK-l) before applying the *^r--. 8) at the gage location. Printedin USAby GP .i'- -^ari-' Enviroamental Protection Apply M-Coat J to tbe gage installatioo carefully fol.Leadwire CoDsiderations When utilizing one active stain gage (quarter-blidge cotrfiguration). should be placed in conduit to prevent mechaqical damageto the leadwire system. 8 After allowing the M-Coat B to air dry for at least two hours at room tempemtue labout +75' (+24"r]. Of couse. Carefully. The coating should be built up to provide approximately 1/4 in (6 rurn) thickness completely surounding the rebar @ig. elch the insulatior with Tetla-Etch compound. and to reduceinstallation time. respectively) to elimimte the need for attaching leadwires at thejob site.if vinylitrsulated cable is used.ftom initial construction forces to unexDected severeloading cooditiors. As a flnal step. Allow this coating to cule 24 hours at +75oF (+24'C). These materials should not be allowed to flow onto the bar strandsof the conducto$. separate the individual (leadwire) conductorsfor a distanceof about 1 n (25 mm) fuom thecabte end and.and CEA-Series straia gagescan be supplied with a preattached three-leadwire cable (Options P and PS. prime the insulatiotr with thinned M-Coat B. providhg data about load effects throughout the ffe of a concrete structure. out tbrough the concrete.if Teflon@-insulatedcable is used. 643-mm dia.Proprietary (130x 17x 10mm)nominal 5x0.Each gage incorporatesa heavy-duty 1}-ft (3-m)cable with 22-AWG(0.7x0.4-mm) Nominalcablediameterof 0.NickeFchromium polyimide Activegagelengthof 4 in backing. alloy (similarto Karma).2in (5 mml (Otherlengthsquoteduponrequest.) leadwires.Speciallengths effectsin the instrumentation sensinggridhelpsminimize temperature ents M'LINE accessory of preaftachedcablewill be quotedupon request. OuterEody. sturdy. 0. cable322-DJVis available in both EGP-Series StrainGagesareavailable Micro-Measurements Ruggedand reliable. of 120or Gridresistance 350ohms. resistances. and350-ohm(EGP-5-350) 120-ohm(EGP-5-120) Specifications Strainsensinggridcastin a eonstr{.Onestraingageperpacl(age.015-in(0.643-mmdla.a three-wireconstructionto the leads.constructed cal strainsinsideconcreteStructures.)stranded tinnedcopperin thickPVCinsulation.leadsof 22-AWG (0. lnc.Thenormalusagerange Ternperature is +25"to +125'F(--5"to +50'C).Exended rangeis -25oto +150"F(-30'to +60"CI (temperature) shouldnot exposure Maximum exceed+220"F(+105'CI Packaging.The grid.has an activegage lengthot 4 in (100 mm) lo( averagingstrainsin aggregatematerials.water-resistant alloyon SensifigGricl. USA .Micro-Measurem for addingcablelengthin the field.r0.is self-temperature-compensated thermaloutputwhen installedin concretestructures.8%.minimizesreinforcement providesprotectionfrom moistureand corrosiveattack.Three1o-ftf3-m. cast within the polymer to minimize concreteto ensuremaximumstrainsensitivily.nominal.mechaniThe EGP-Series EmbedmentStrainGageis speciallydesignedfor measuring of a nickel-chromium The sensinggrid.A rugged s-in (130-mm)outer body of proprietarypolymerconcrete of the structure.4in Oable.rcti@n. (100mm). material. polymerconcrete. 27777 1.) Range.and resistsmechanicaldamageduringpouring. mn gages.Careshouldbe takento (a)securethe ..To obtain the measuredstraincorrectedfor leadwireresistance.Whilethe Embedrnent . solderedconnections are highlyrecommendedfor all splices.EGP-Series Embedment Gagesare designedto gagein the desiredlocationand orientation and.643-.StrainGageThermalOutput and Gage Factor Variationwith Temperature. GroupTechNoteTN-504. SensorAlignmeit TheEGP-Series Embedment SlrainGageis designed to measurethe axialstrainalongits length. TemperatureFlange accuratealignmenl duringinstallation is necessary.Accordingly.independent thermaloutniquesshouldadequately embedthe gagein most put correctionsmay be necessary.for For thg mostcommonlyusedstructuralconcrete(Type oplimumresults.normalpouringtechoperating temperature ranges. To preservetemperature compensation. tion trom moistureand otherenvironmental contaminants.CableSplices \ EGP-Series Embedment Gagesare shippedwith1o-ft (3-m)cablesin orderthat mostleadwiresplicescan be madeoutsidethe concretestructure. or dividethe indicatedstrain bv D.{b) tie virtuallyeliminatelhermaloutputeffectsovera wide the leadwiresto any availablesupportbetorethe contemperatule rangeand generally requireno correction creieis poured. EGPbridge. lor completedetails.Alligator clips. See Measuremenls cases.bananaplugs. lnstrumentation gagesare designedto providefor reliable EGP-Series grid in the Embedment The strain-sensing Gageis destrainmeasuremeht underdemanding environmental signedto be connected to the measuringinstrument as conditions.The eiectricalconnectionsalso requireadequateelectricalinsulation. 3500). is the resistance of the wire.1996 .The cablewill attenuate themeasured strainasfollows: D= RG RG+Rc where:Fc = gageresistance (120or 350ohms)and F.)cablesuppliedwith EGP-Series the resistdnbe is approximately 0.for theseeffects. Detailedinformation abouttheseand otherstress/strain measuring instruments is available fromourApplications Engineering Department.employed to Seriesgagesshouldnot be exposedto temperatures minimize thermaletfectsin theleadwires.specialprecautions arerequired. abgv. nectedto the measuringinstrument in accordance with the manufacturer's dlrections. as wellas protec. zero a singleactivearm (quarterbridge)in a Wheatstone stabilityand otherperformance characteristics.wire crimps.The three-wire systemof leads.or overgreater straintransJer fromthe structure. dia.and othertypesof mechanicalconnections shouldbe avoided. shouldbe con(+105'C).Whenspliceswillresideinsidethe concrete struc' -' tureitself. gagefaclorat the package eitherset the instrument gagefaclormultipliedby D.For lypesofrconcrete Gagemustbe wlth thermal entirelyencapsulated in concreteto ensurecomplete characteristics differenttromType3500.Becauseof the relalively smallresistance changesinvolvedin slrain measurements. Printedin USAby GP May.17ohmsl.q'+220'F The Model P-3500PortableStrainlhdicatorand/or2100 Systemare I idealfor measurements withEGP-Series Embedment StrainGages.[Forthe 1o-ft(3-m)22-AWG (0. Reference10 J J J I _l I I l . to any measures ble to applythemosteffectiyenoise-reduction particul. ElectrostatlcField NoiseSourcesandPickupMedia consumes.If not controlled.4tr4 in severecase. .An4 in geaeral.andthecloserthesEaingagecircuit!o theelectrical device.anddescribesthe rouiesby which the noiseis hduced into strain gagecircuits. switches. noisetypes.Inc.varyi:rgwith the noise-coupling nism.The informationin this technical note is equallyapplicableto botb amlog ad digital systems employingdc anplifre$. motorsaDdmotor stariels . or without curcnt flow. . connectors.-i r^ Noise Control in Measurements T . . It alsoappliesto systemsusingcarrier excitationandcarrieramplifiers..etc.by which chargesof conespondingly alternatingsignaredevelopedon auyelectricalcondocto$subjected to the field (Fig. tsansformers StrayCapacitanc€ Jr i* AccumulalsdCharges Signalwlre Fig. . . and thus requiredifferent rneasues.the higherthe voltageor curreatlevel. This technicalnote identifies someof the more corlmon noisesoEces.d @Copyright MeasurementsGroup. or traDsmitspower is a potentialsourcefor causingnoise in staio gagecircuits. It shouldbe notedthat th€ teatmenthereis limited to noisefrom externaleleccicalard This notedoesnot covereffectsftom uuclea! magneticsources.Followingthediscussion mechaic rnethodsare giveu. 9.with.the greaterwill be theinducedooise. J NoiseControlin StrainGageMeasurements Introiluction i mustoftenbe madei[ thegesenceof Suainmeasurements electrielectricand/ormagneticfields which cansuperimpose cal noiseon the measuemeutsignals. fimt to unde$tand ratio.andmaxisignalsaltogetber. . or thermalsources. In orderto controlthemhe level. 1).arinstumentationproblem.with &is understanding.Electrostaticnoisecoupling. . for noiseavoidance..tbe noisecanleadto iDaccuateresultsandincoFectinterpretation canobscuretle strain of thestrainsignals.mostof thecommon uoise-reduction noisesourceslisted aboveproducecombiaatiolsof the fwo problem.s. acPowernnes . .whichcancomplicatethenoise-reduction of voltage by thepresence Electrostaticfields aregenerated .Udorfiroately.it is necessary mizethesignal+o-noise of electricalnoisq aswell as the the typesandcharacteristics it is thenPossisourcesof suchnoise. 1 . Altemating electricalfields inject noiseinto straingagesystemsthroughtle phenomenon of capacitfuecoupling.nor doesit considerthe effectsof variable widng or contactresistancecausedby slip rings.Followingis a list of commonelechicalnoisesources: . relays Seneraiors rotatingandreciprocatingmachinery arcwelders vibrators fluorcscentlamps radiokansmitters electricalstorms solderingirors into Electricalnoiseftom thesesourcescan be categoriz€d two basictypes:elecEostaticandmagrctic. . .The two tyPesof noiseare fundameutallydifferent. Fluorescentlighting is oneof the morcconmon soucesof electrostatictroise. 1992 All Rlghis Fleserved. Virtually everyelectricaldeyicerthich generates. specifof noisesources. c) If feasible. 3). the stain gage hstrumetrt selectedfor use should incorporate a simple. and observenoise. For tbis purpose. turtr next to the oxtemal circuitry. 2. and may causethem to be cut by adjacent sensitive conductors. The following prccedure can be used to toubleshoot a system for noise: Electrostatic Source StrayCapacitance 1. This may be due to gage seu-heatitrgeffects (seeMeasuremetrtsGroup Tech Note TN-502. reduce amplifier gaio aud comPensate by increasing bridge voltage.dre noise is due to somethbg associatedwith the loading system such as a motor qeating a magnetic !eld. any subsequentchangeio output. If possible. In the prcsenceof an altemating field.nimize the effects ofnoise. a conductor moving through the earth's magnetic field has a noise volt8ge generatedin it as it cuts the lines of flux. As a result. independendyof any strai. atrdfor magnetic noise.IJ excessivenoise exists. Consideration should be givetr fiJst to noise sourcesaffecting the strain indicator itself. is zerodrift. Since most irons and steels arc feco-magnetic. Electrostatic NoiseReduction Detecting and ltoubleshooting Lo order to effectively assessthe presenceand magnitude of noise. remove the load ftom the test part and apply excitation voltage to the bridge circuit. Eagnotic ' lines of flux must be "cut by the conductor Electric generators firnction on this basic principle. this is an indicatioo ofa poor gound and/or radiof. 4. If additional noise is observed. Once coUected.amplifier input with about the same input jmpedancethat the anplifier normally senses(rypically between 120 and 1000 obms). 5. and for experimeltally modifying these methods to m.thesecharges must be drained otr to a satisfactory grcund (or rcfererce potetrtial).ificaat feature .€A. 3. not noise. 2 - Electrornagnetic noise coupling.---!w!{swuvj i-r-. etc. a.an^A ruevr^!rvq!v. In order for noise voltage (enf) to be developedin a conductor. With tlle excitation switch set to ofi cotrnectthe gageor tansducer circuit (including leadwires) to the instrument. b) Check for line. 2). instance of the latter. -2- Conductors Ground Capacitance Shield-lo-Cable Fig. This reFesetrts a very powerful tool for evaluating the effectivenessof shields and ground. If not alreadyknown.a switch for removing the excitation ftom the Wheatstonebridge. Apply a load to the part uDdertost (with excitation still of0.3 . If not prcvided q/ith a low-resistance drainage path. Sinilarly.-^.lt trrctions by capturiag the chargesthat would otherwisereach the signal wiring.or other time-dependelt resistance changes. Of course. if gradual. moving machine members redirect existitrg lires of flux. voltage will be induced into any statioaary conductor as the maguetic field expandsaad collapses (Fig. If the output changeswhen the insbument chassisis touchedwith a finger.usignal. . Series-lnduced Voltage(Yr> Yt _-\ Fig. discomect any sttab gageleads. With such a control. All MeasurementsGroup sfiain gagesignal conditioners are equipped with this important featue. MotoE and transformers are examples of the former.("mains]') radiated noise. sometimesrefened to as a Faraday cage. isolated ftom all ertenal circuits.Elecftostitic shielding. ald the earth's nagnetic field is ar. Sfiain Gage Excitation Levels) . but very sig!.) as observedon a readout such as au oscilloscope or lecorder. Havhg eliminated or satisfactorily minimized noise pickup by the instrument. After balancing the bridge. such as that surounding a 50/60-Hz power line. the instrument output canbe easily checkedfor noise. a) Check for ground loops (more tbaa one connectiotrof the system to gIound). irches of deflection. LVr +v2 The following sectionsof this Tech Note give recommended noise-reductionprocedues for electrostaticnoise. deterrniaethe tolerable levels of noise in output uaits (Eillivolts.nyadditional noise picked up in this step is attributed to leadwirc aud/or gage pickup.Magnetic fie1dsare ordinarily created either by the flow of electric curreqt or by the presenceof permaneBtmagnetism. or the motion of the gage or wiring (generatiug emf). The simplest aad most effective barrier agahst electrostatic noise pickup is a conductive shield. aEd terEfuate the S+/S. signal conductorsin the viciuity of moviog or rotating Eachinery are generally subject to troise Yoltagesftom this source.. the chargescan be coupled into the signal conductors through the shield-to-cablecapacitance(Fig. it is evident ftom Fig.ldbe grounded at one end. for gageinstallations which will opemte at elevated temperahues. The troise transfer can be minimized by employing an instrumentation cable composed of ildividually shielded pairs . and one pair for the signal. preferably from the iNtrument-etrd of the cable: conductor-toground. or common-mode voltage. . It is oot uncommon to have sFaitr gages i$talled ou nominally grounded test objects which.fier system (for example. instead. . Achievement of noise cancellation by the method shown in Fig.or tbree-leadwire). 2 that a $adient in magneticfie1d inteosity exists with respect to distance ftom the cffrcnt-carryiag power line. and to the effects of nearby power lines. i I -3' '[!''. somestrain gage hskuments (for example. b. to ensue that noise voltages are induc€d equally in both sides of the amplifier input (Fig. signiflcatrt levels of aoise can be iaduced into sensitive conductorstbrcugh both magnetic and electrostatic coupling. Correspondingly effective. the insulati6! resistanceftom the gage to the specimen should be measued with a megohm meter such as the Instrumelts Division's Model 1300 Gage Installation Tester A reading of 10 000 rnegohms is normally considereda minimun for satisfactorysystem operation. it is always a good practice to make certaiu that the specirnenis properly grounded aud that leakage between the gage cilcuit aEdthe specimenis well within bounds. Belden No. the voltage difference between the conductors and shield is essentiallyzero. with this arrangement.With runs of 50 feet (15 /z) or morc. both shields should be gounded at the instrumetrt eud of the cable. this leakage can cause noise transfer from the specimetrto the gage circuit. 4.foil shields give 100 percent cable coverage. and the excessive leakageeliminated to avoid potential noise problems. Although commonly higher in resistance. Another often-overlooked source of noise is leakage to ground tbrough the stlai! gage and/or the cabling.one paft for excitation. Tbe bnided-shield construction Provides about 95 percent coverage of the cable. a fully guarded ampli. all conventional strain gage bridge arrangemeuts . half bridge. This type of construction is embodied iD Mido-Measuements Type 422DSV cable. Pdor to connectbg leadwires to the strain gage.I Tbe two most popular q4resof cable shields arebraided wire a-ndconducdve foil. twisted) foil: Micro-Measuremens Type 422-DSV Whert long reachesof multiple conductors are run adjacent to eacb other.thereby inducing equal noise voltages which will cancel each othe!. To minimize this effect. After cable placementand connection at the gage-endof the cable. 4). which shou. there can be signif. and fir1l bridge . and coaductor-to-shield.Noisecancellationby ampffier common-mode rejection.and there is minimal noise transfer The result is a very quiet shield. atrd arc also easier to terminate. Electromagnetic NoiseReductibn The most effective approach to minimizing magnetically induced noise is not to attempt magnetic shielding of the sedsi tive conductors. but. This is also true for systems which employ the "rctated" or nonsymmetrical bridge ctcuit. The shield-to-conductor capacitalce can alsobecomesignificant for long runs. the effeccivecapacitanceis decreased. 4 . the driven shield is connectedat orfy one end to the driven-guardpin on the instrumentbput coonector. to the stafui gage wiring. InputNoisB ldeal Output Noise Vs=0 Amplifier InputNols6 Fig. and is characteristically low in resistarce.Measuremeats Group Instuments Divisiou's Model 2200 and 2400 Systems).quafier bddge (two. Measuremeuts Group Instuuments Division's 2300 System) incorporate a featwe called a driven guard. Even though bridgeexcitation cooductorsmay carry only a millivolt of loise. 8?30 cable has the conductor pats sepantely twisted. a significant ponion of the residual roise cao be coupled from even a well-grounded shield to the sensitive conductors. since even supposedly well-grounded specimens may carry som€ noise. dive\ gu:td (also klown as a d/iven s&ieldl functions by maintaining the shield at a voltage equal to the avemge signal.In tight of theseconsiderations. the common-mode voltage of the bridge excitatiou supply and the siglal input terminals "float" to the level on the guard shield. the following resistancemeasurementsshould be made.icantcoupling to signal cotrducton to produce potentially troublesome rnicrovolt-level noise itr those conductors.that leakageresistance tends to decreaseas the tempenture increases. An4 ofcourse. Connectlng the shield to the test strucfl[e or source of common-mode voltage at the gage installation site can provide very effective troise rEductiotr since the voltage between signal conductors and the shield is minimized. Electomagnetic coupling betweotrexcitation and signal pairs caa be reduced somewhatby usirg a cable drat has its conductor pairs twisted on separateaxes.Readingsbelow this level are indicative of a possibly troublesome gage installation wbich cao deteriorate with time and sbain. have uoise levels expressiblein volts. since the capacitanceis proportional to the gable length. If excessive. however. problems with crosstalk betweencooductors cal be encouatered. 4 requires that the amplifier exhibit good common-node rejection characteristics. A. on the average. including one pair shielded with foil. these resistancesmay be somewhat lower tllatr the gage-to-specimenresistance. Therefore. Tkisting the signal conductors together tends to make the distancesequal.Atiention must also be given. o o braided: Mi{o-Measurenents Type 430-FST (four conductoE. iD fact. for proper operation. but cables with significantly lower resistancesshould be investigated. any stlain gage installatioTlon a conductive specimenforms a classic capacitor which can couple noise from the specimerl to the gage. ften using sucll cable (those having separate shields). Becauseof disnibuted leakage. Whetr analyzed. FoUowing are cosr. The seriesnoise voltages(yj atrd y2) induced in the signal wires will therefore dependgreatly upotr their distancesfrom the currentcarying conducton. It is importatlt to note that. shield+o-grouad. It sholld also be kept in mind.mercially available examples of the fwo types of shielded cable: .reduceto the samebasic circuit shown in Fig. the magneticfield strengthsradiated by power Linescan be rcduced by twisting the power conducto$. Since.The driveu shieldis ordinarily surrounded by a second shield. For example. have sufficient twisting for most apPlications.Handling excesscable. and/or at intermediate points . before significant troise redoction is Heavy-walled iron conduit ca! also be used to proreductionin mametic noisepickup.It will be miniroizesthe susceptithe prefeFedarrangement iltl ilil v Signal apply loop.there high-perneabililty alloys (mu-meial@. atrd uoder no circumstancesshould be disposedof by winding into a coil as iUus7a. 5 - affectthe s'ensitiviryto magneticpickup. as shown in Fig. Cunent flow it sttch ground loops cal induce noise in tbe sigral-caftyitrg conductols through tle samephenomenonthat occuts in a tlansformer. For the samereasoq flat ribsbould be avoided.eldimpedanceftom one end to the other can become significart.are particularly suited to this fyPeof aPPlication. S'-Small i). The reasonfor this is that the ground points may be at different voltage leyels.with copper-coated Ebs. and the result is a noisy shield. t. and transfome$' l t!l MediumArea twistingmaybe requiled. Magaetic shields are made from highmaterials such as iron and other ferro-magnetic At the r€latively low 50/60-Hz power line frequencies etrcounteled in magnetic noise problems. Multiple-point goutrd .Tabs arr ExcessFoldedTightly ln Halfand Coiled ExcessEliminated (c) (b) Bert Better Fig. 6. when shielding against audio-frequency electrostatic noise Oelow 20 kHz). genemto$. rather than through auxiliary terminals. )o lo at I | IR i1\ (c) Best Signal Cable comparison. and to bend or shunt the magretic field around the co[ductor than eliminate it. 7 . tl }€D b RI XP FI I+D lL\\_ CoiledExcess (a) Poor il[ (b) Better (c) Poot the excitation leads and the signal leads. grounded does rot function as a barder to magnetic Magnetic shields opemte otr a different principle.and it may be to use a special woven cable asdescribedlater. it is not good Facdce to gound the shield at morc thao otre point. /Rlbbon \ cable alea betweetr the wires. it in Fig. 3tandardtwisted-conductorcables.Preferably at points near any localized sourcesof electostatic noise.for instance) have been developed specifically for magnetic shielding These are effective in much thinner sbields than with Wher faced with the apparctrtnecessityfor magnetic attention should always be givetr to reducing the at its source. the gageselection and the widng arrangemerts G) Best Fig. bafffotners can readily be to minimize the leakase flux. particulady with high-ftequency noise sources. If excesscable length cannot be avoided. CEA-Seriesgages. However. cotrnectionsshould be madedirecdy to tbe solon the gage.Ioblems. 5 .andis usein magnetic the case for elechostatic noise.1 in TwlstedPairsOn SeparateAxes \ /r/ is very protreto noisepickup. excess lengths of inPut be elimbated.As il Fig.The sar::ecablingconsideratious Fig. Elechostatic Fields Generally.such as Belden t. for lotrg cablesin severenoise esvironments. SevereNoiseEnvironments preceding two sectionshave treatedthe standardmeth- ofnoisereductionapplicableto themajorityof instrumenI. at least. be folded in half and coiled asindicatedin Fig. such fouDd close to motors.."^ K n attaching leadwircs to a suain gagefor operation in a field. In addition. As an example. When this occurs. car the pickup.For panicularlysevereappliconventional twisting may be inadequate. the more twists per urdt cocductor le[gth.. shield thick- Gage selection and wiring technique. (usingcommoniron for example)on theorderof 0. the noise chargescaptured by the shield no longer frnd a low-resistaoce drain to ground. 7b so that current loop is iltimately accompanied by a lll ctose ltr . Wben necessaryto use this tyPe of optimal conductor allocation.However. Howetrvironmentswith high magnetic field gradielts. 6 - nm) arc r'eed. causing currcnt to flow throug! the shield..This sectiondescribestechniqueswhich may uecessarywhenveryhigh noiselevelsare anticipated Ludlum SieelCo. the shi.ed. Improved shield performanceunder such circumstances cao often be obtained by gounding the shield at both ends. a simple. is largelyinsensitiveto magneticfield gadients. For instance. or segmentsof the shield between grounded points. As a rcsult.Referringto the wireftom eachplane)areconnected fi.atteotionshould andshuotcapacitance." . since this will result in the thiraest glueline. ElectromagreticFielals As with electostaticnoisepickup. The trvo shields should be together only at the instument end of the cable. Cotrductive epoxy compoundscan also be used for this purPose. a double-foil shield should be used over the strain gage. noise Pickup can also occur in the gage itself.asseeuftom thewirc end. groundconnections. aIId insulated from. the H-Series. In such cases.orldisavailableftom: MagneticShieldDivision. For tbis purpose. are inainsically quieter than latge gages. the gage shield.Wown cablz to reduce severe electromagnetic radi' ation and pirkup. andshouldbe asshortaspracticable.Eected A word about ground connectionsis in orde!' It is important are characterizedby resistanca. generators.nductive stacked gages . On the other hand. Available from Micro-Measurcments are two types of dual-element.eliminatesthespiralinductiveloops(Fi. with one stacked directly above. when gagesare installed on machinery or other larye. The dual-element gage is intended to fuDction as one arm of a Wheatstonebridge ctcuiq and the bridge is usually completed with anoth€r gageofthe sametyPe. If the cable has two shields.but the Miqo-Measurements M-Boud 600i610 adhesive system is recommendedfor bonding.an impossibility. Care must also be taken to make certain that the shield does not form a short ctcuit to the gage wiriDg. coD.and rhistypeof cable wircs3 atrd4 to form theother.(explodedview) .a 6-ft {2-n) copperrod can be driveninto theearthto establisha local ground.In irtenseelectromagnetic gradients(near motors. Even though tbe strain gageis much less ftequendy the signficant medium for magaetic noise induction than the leadwires.and similar equipment).both parallel andperpendicularto the cablelength. different gage pattens have differing sensitivities to noise pickup.The cableis known as Inter8 Weove. conductive test objects.the optimum grounding schemecan be determined.noni. a simple electrostatic shield can be fabricated by forming an aluminum-foil box over the gageand the ushielded leadwire termioations. ideally at least.the foil should be electrically iosulated ftom tbe machine. As sbown in Fig. cousisting of two idetrtical gdds. This anargement is particulady effective agahst magnetic field gradients aud their comporents parallel to the test surface. and3 & 4 Connected Construction Finished Cable Fig.gure. and the sPecimentogether. Wlen needed.g-8). SeeCatalog 500 for details. E seriesNon-InductiveGage.'rg the gages.connectio i nay also be necessarywhe[ ndio-ftequency interfereace (RID problems are encountered' At these frequencies the shield. and placenent of the grids as close as possible to the specimensurface. Formsxinum cancellation of electrostaticfields.woven.5.An endview of a conventionallytwistedpair canrevealthereason for pickup. But the machine should be grounded with a heavygaugecopper wile (at least 14 gaugeor heavier dependingupon apptcation) cotrnectedto the single-point ground rear the imtrument. Although the leadwtes are ordinarily the dominant medium for noise inductioo in a strain gagectcuit. 740 ThomasDrive. To be quality given of the alwaysbe to tbe effective.Illinois 60i06.theleadwirescommody represetrtthe pril1cipa]souce of magneticnoiseinduction in fie1dswith steep straiogagechcuits. inductance. the tret noise pickup is lessthan for a gagewith one tab at each end. the noise inducedin the assemblytends to b€ selfcancelling. If the gaged specimen is small and electrically conductive.with rrore closely spaced grid lines. Iu severenagnetic fielcls. care must be exercised to prevent the occunetrceof gound current loops in the sbield.wires 1 and2 aregaralleledto form oneconductor. if the gage has both solder tabs at one erd. especially thosewith steep gadientsin field intensity. ordinarywire-twistingtechdquesmay proveinadequate. evenif the inducedqoise werepreciselyequalin both wires the amplfier noiseouput wouldbe zeroonly if the amplifierhadinfinite common-mode .or with a fixed precision rcsistor Standardpnctices are followed when install. pairs of wires (composedof one in parallel. Bensensville.In orderto mini' rcjectiotrcharacteristics noisevoltages.a special. additional measuresmay be required. the difference in noise sensitiyity results ftom the relative size of the inductive loop area in each case. then.As indicatedir Fig. PerfectionMica.If the nearesteartbgroundis too lemote.four-wirc mizecommoq-mode cablehasbeendesignedwhich.a coinection to groundshouldbe madewith heavygaugecopperwire. at Terminals Together Wires1 & 2. 8 . the other By contrecting the upper and lower gage elements in series so that the curreat flows in opposite directions through the two grids. By expedmentally grounding the shield al numerouspohts along its leDgtb.liaear H06A-AC1-125-?00 and a thftegagerosetteH06A-AD3-125-700. .It is also worth notitrg that smaller gages. 4.Soconnected. aluminum tape with conductive adhesive should be used to conn€ct the cable shield. catr display antennabehavior. Micto-Measurements has develoPed a special gage configuration. i0:59-65(i978). October1969. 1967.8. Krigman.In addition to the stlain gage size and Pattem.strain gagescan also be shieldedftom electfomagoetic fields to some degree with a magnetic shielding material such as mu-metal. 3| 4 (1982).EI€cf. NewYork: HaydenBookComparLy. Thermocouplesand Leads.. Coostantaq however. Aprn D77. Of course.R.No. "SpuriousSignalsGenerated in StrainGagos..No. "strain GagesOperatein 50 000-GaussMagueticFields For FusionResearch. No. the selection of the gage gdd alloy should be given careful consideration. Freynik.Jim.F." InstrutnentatiotTechnology24. "Common-mode Level DataAcquisilion. 69. constantan ard Kama-type alloys are usually selectedfor such applications. If the grid alloy is magnetic. "GasketsthatBlock EMl. Sitter. *Available from: Stein Engineeing Senices.Similady. bibuogaphy).magnetic field. 1973. The Karma-tyPe alloy is ordinarily preferred for cryogenic service becauseof its generally superior perfornaace il maguetic fields at very low iempera res." MachineDesign47. Instrunents& Control. 5602 E. 17. Klipec. SuggestedAdditional Reading for LowRejectionTechniques Coffee.2nd Ed."AAUISE PublicarianNo. New York: Hayt. Monte Rosa. Germantown. will undergo spurious resistarce changes. 12:21-34G9'17). W. PeterK.. EngineeringElectromagnetics.nGagesfor Stuctues CryogenicStressAnalysisof Super-Conductirg in High MagneticFields. J."/n-Tech32. +Skin.Isoelastic alloy.Practicdl Designfor ElectromagneticCotnpctiDifttl. "I{ow to Avoid NoisePickupon Wire andCable. No.19:74-77(1975). Stemming fiom their comparative freedom from magnetic effects.et."EMI ShieldingandProtectiveComponents. 'RFI ."htsftuftLentation No. W}Ien high-ftequency Iields are encountered. McDermott. if magnetorcsistive.be sule that the material is suitable (high permeability) at the anticipated frequency.Inc. No.. October. the gfid will try to change length in the magnetic f..B. No.) II.R^1p6.S.J. and.H. a1.reld.. Phoenix. New York: JohnWiley & Sons. "The Responseof Transducers to Their Environment.wlat It Is andHow to ControlIt Part II: Techrclogy 25. Inc. Reductionof Intederelce.'omagnetic Don White CoNultants' Maryland: Yol.D."Nickel-CbromiumStrai. at cryogenic temperaturesand in high roagneticfields (7-70 Tesla) becomes severely magnetoresistive.M.1977. if the alloy is magnetostictive. R.7:4549(1977).E. InterfermceandCompatibility' Wldte.PeterK.Arizona 85018 November 1999 -6- Printedin USAby GP O .ever this will be ineffective if the sourceof the magnetic fleld is beneath the sEain gage. Ir. Two or more layers of the shielding material may be required to effect a noticeable implovement."Epsilonics(pubiishedby Measurements Group.H.Systerns *Stein.. 3. Sevednsen. it will be subject to extraneousPhysical forces ir a.P. should not be used in magnetic fields.(Extensive Electrical Noise.The Problemof SignalandNoise.Groundingand ShieldingTechniques Instrumentation. 16: 165-176(1979)." Proceedingsof the Seventh Symposiwnon Engineeing Probkms of FusinnResearch." EDN U."Lf/MSE PublicationNo.1977.Alan "Soundand Fury: The PersistentProblemof t:9-20 (1985)." 50. in Morrison. Ficchi. since it is both strongly magnetoresistive and magletostrictive... McGraw-HillBookCompany..R.. When necessary. for exarople.. 1971. Reference11 . copper-coated tabs for convenientleadwir€ atlachmont.coupledwith water.codosive Eedia sc 325 Ijltsa-t€mleraireEnvirorsents to 950'F static (1200"F for short tidles) with protectionftom colrosive tDedia sG 425 Eebedrdent in Concrete. leads idsulatedwih fiberglass(SG 128) or magrcsium oxide (sG 125) fo! the most severeapplicatioos Nickel chromealloy Integral Irad Stratu cagesqd.Integralthree-tabprinted ckcuit terminalsfor convenientleadwireattachment. buildirgs.the battery'powered whereno powerlinesare available. be usedunderlieldcondruons A temperature-controlled solderingpencil. pilings wheaeverhudidity. requestBulletin302. specialtemPelatue ft4es. 120 Q self-coEpensatedgageswitb prewaterproofed. magrcsiumoxide insulated idtegtal leads Nickel cho6e alloY Flexlead SEain Gage.for dodels or firll size stuctules CG 129 sc 328 Ilescriptlon Flexlead Straitr Cage'.up to Cryogenic Temperatures 650oF.completely encapsulatedin a tiberglass-reinlorcedepoxyphenolicmalrix.gasketedcase. rugged installation ptocedue is requAed ExteDdedTeropeEhrreRanges* to 650"F statico! 1500'F dYrlamic even when water. are available' h Basic gagetypes(wittrout integral leads)are ata able.capacitancedischargespot welder. Nickel. WWFSeies Weldable Temperaturc Sensot: High-puritynlckelsensinggrid.eliminating time. For furthet detaiE.and withoutadheis ac€omplished Installation Thesesensorsareeasyto installand requireminimalsudacepreparation.operaiedtrom the main battery supply. {lexible etched Teflor@insulatedleadwires. etc. Weldablegagesare precisionfoil sensorsbondedto a metalcarier for spotweldingto structures. tbreecodductor.I bridge ft-W to gage for static strain measure-Erents 1200'F. .In most casescan be contouredto radiias small as 112in (13 nm).gt.shieldedcable IDtegm.+ bridge verioDs of SG 125or SG 128gabepmvide optittruE therEal codPeEsationitr the cryogenic or subzeroranges:also awilable ddft at 650oF for ni.InstallationradiusgeneralIy limited to 2 in (50 am) or larger in thg directjon ol the grid axis.ini'ilg Platinum hrlgsten alloy htegral L€adStrainGages.] bridge. otlrcr temperaturera[ges available Nickel chrome alloy ' CourtesyofAiltech.ffiSeEdmhEe SfisaEmffimggesamdlTempera€e$seSesnsos"e components. Rugged. t""d. hermeticriy sealedcables a'' Dot '"quireal Some basic gages are usezu to 1800"F for dFamic " 350 Cl gagesare available. .is an integralpart of the Model700.viayl ilsulated. LWK-S1 es Weldable St@in Gag6. sives. or a siltrple. rain.I bridge.Suppliedin a rugged. direct ieEersion. @Registered Trademarkof DuPont Fffiode57S$ Fortable Straim Geqe WfeldFng and SclderinE UmEt The Model700 is a completelyportable.Very tlexible. The lightweightpencilcan be adjustedio a wide rangeof tip temperatureslor both gage solderingand leadwiresplicing. chromiumalloysensinggrid completelyencapsulatedin a fiberglass-reintorced epoxy-phenolic matrix.Hydrostatic testing.They provide featuresof luggednersand simPlicity of iqst"nadon wten Li.llJld SuatuCageqd. equippedwith staidess steel jacketed. IEc.6teamor coarosiveEedia sufiounds gagcs Prelerred Gage Typet Filament Malerial SG 189 Nickel chroee alloy SG 125 sG 128 .Integral three-wire lead system consists of 10 in (250 mm. testprograms Theyare alsowellsuitedto laboratory heatcuringproblemson massivestructures. testingandminimalinstallation requiringelevated-temperature CEA-Series Weldable StGin Gage: Constantan alloy senslng grid completely encapsulatedin polyimide. Table7.designedfor direct eBbeddent in corcrete. 120 q self{ompensatedgagesv/ith herEelically seale4 stainlesssteeljackEei cable.1 StrainGage SelectionCharli Applications ShaitrMeaslrementfu the Field blidges. sGam. of weldablestraingagesand temperature designedtor efiicientinstallation unitcan sensors. G180'F. J II Reference12 .i I I i I I I l . BOX2ZZ. (919) 365-3800 TELEPHONE FAX(919)365-3945 . RALEIGH.USA NORTHCAROLINA P.O.2I()()SYSTEM f Strain GageConditioner and Amplifier System fnsfuuctionManual . 27611. DIVISION INSTRUMENTS MEASUREMENTS GHOUBINC.-l I . 2 2710APowerSupply(AC-Operated) 2. 4.. 4. .. .10 Excitation 4.12BridgeBalance..7 OutputLimits .4 InternalAdjustments 6.. 6.2 DC Power 4.3 Field-Replaceable Components 6.. .2 Servicing . .0 OPERATINGPROCEDURES.5 Millivolt Inputs.1 2120AStrainGageConditioner 2.. . . . 3.5 Schematics t7 t7 t7 l7 18 18 Warranty APPENDIX Model2130Digital ReadoutandModel 2131PeakReadingDigital Readout oCopyrightMeasuremenG Group.8 GalvanometerMatching 4./2l'll PowerSupplies. .1 General 1. A-1 Printedin USAby TD .4 Wiring Considerations 4.14Noise 6 6 6 7 E E E 9 9 10 10 l0 l0 1l 1l 5.1 2ll0A.. 3.13Gain 4.4 2150Rack Adapter 2. .3 2lll PowerSupply(DC-Operated) 2.3 Input Connections . 4...9 Operation 4..1992 .. 4.3 ShuntingInternalDummy Gage(120or 350O) 5. 5.6 OutputConnections.5 2160PortableEnclosure 3 4 4 4 3 .0 DESCRIPTION. .0 SERVICINGDATA 6.. 3 J 4 f.0 SPECIFICATIONS 2.11 Amplilier Zero . .INSTRUCTIONMANUAL MODEL 21()O STRAIN GAGE CONDITIONERAND AMPLIFIER SYSTEM Page 3 3 3 1. 0 C o N T R O L S.5 OptionalRemote-OperationRelays t2 12 12 t2 l2 16 . . 4. 4.I SetupandAC Power. .. .1 Equations Internal HalfBridge(350O). 1.2 Shunting 5. .2 2120AStrainGageConditioner.Inc. ..0 SHUNT CALIBRATION 5. 4..2 SignificantFeatures 2. .4 ShuntingActiveGages 5.. l 4. 6. 4.1 CustomerModifications 6. . Left to Right: 2110APowerSupplyModule.2131 RackAdaPler 2150Ten-Channel -2- .Eight-Chrnnel2100System Two-ChannelSystemin 2160Porlabl€Enclosure Digital Display .2111PowerSupplyModule.2120AConditionerModule. 4. inputs. Bridge-completioncomponentsto acceptquarter(120O. 350O and 1000O).half.) -3- *Referred to Wut **Refered to otttput- .24ano-loadto l20O load(107alinechange). LoadRegulation:t0 . currentlimitedat 3140mA.complete with wi. dc to 5 kHz:-0.5 to 12 Vdc).1Hz to 100Hz..r€(quarter.ring.dummy350Oanddummy gagesandthree-wire l20O completion calibrationcapabilityprovided. .eor half or 3500 full t60001.and full-bridge inputs to eachchannel.A systemwould be comprisedof: a) One or more two-channel21204 Srain Gage Conditioners. t40 nA max.with ten-tumcountingknob. tem for generatingconditionedhigh-level signalsfrom strai! gage inputs for display or recording on extemal equipment.5 dB at all gainsettings andfull outPut.I 2120ASTRAIN bAGE CONDITIONER NOTE: Thesespecificationsapply for eachof two iodependentchannelsDermodule. BALANCE: Nlethod:Potentiometdc. b) One or more 2110A PowerSupplies(eachPower Supply will handleup to ten channels. 2 g. TemperahrreCoefficientof Zero: tl pVl'C RTI. LED null indicatorson eachchannel. dcto 50 kHz:-3 dB at all gainsettings andfull output. fiye 2 120A Conditioner/Amplifiers). CapacitiYe EXCITATION: Type:Constartvoltage.Cl(balance Input Impealance: limit resistordisconnected).see6.e. . 200pvrms at 0.50r17otypical.1Hz to 50 kHz. -10" to +60'C (after30 minutewarm-up). . Rejection:(dcto 60 Hz) Common-Mode CMR (dB) GainMultiPlier 6'7 x2 8'7 x20 100 x200 Output Range:tlov (min)atil00 mA. Short-CircuitCurrent: Lessthan40 mA max. I.to acceptthe abovemodules.See provision.continuously directreading.1Hz to 100Hz.15lrF.or full-bridge acceptquarter-. or up to ten channels when maximum bridge voltage and output curent are not required). by intemal Range:(conhgured Extended jumper. .Intemal straingageor transducer half bridge.5to X10..i. 2.always active.I. Range:r2000p€.GainstepsX2. NoiseRTI*: (3500 souceimpedance) I pV p-p at 0. X20. .1Hz to 50kHz.t2l0 PVI'C RTO.1 GENERAL from Protection:lnputis Protected damage of inputsup to t50V differential or t25V comnionmode. X200.1Hz to 15kHz. X0. 80 tr V p-p at 0.O DESCRIPTION 1.Jcfor dummv1000f.5to 12Vdc (continuously for eachchannel)with l20O adjustable full-bridgeload. NoiseRTO++: 50 pv p-p at 0.2 SIGNIFICANTFEATURES The principal featuresof the systeminclude: . one or more 2 I 1i DC-Operated Power Supplies(each2111moduleis capableof powering up to eight channels. 14000P. Loading:Up to 0. Gain: 1 to 2100. c) One or more rack adaptersor cabinets.5 dB at all gainsettings andfull outPut.e. dc to 17kHz:-{.25 x 19 in ( 133x 483mm) flck space.Vrmsat 0. Optionally. Noise:t2 mV p-p dc to 20 kHz. Compactpackaging. All suppliesand outputsshort-circuitproof with cunent limiting. or disabled by bridge)rangesselected irtemaljumPers.1Hz to 10Hz.1Hz to 10Hz. FrequencyRespons€(min) i NormalRange: dcto 15kHz:-3 dB at a1lgainsettings andfull outPut. 100irvrms at 0.0 SPECIFICATIONS All specificationsare nominalor typical at +23oCunless noteo. INPUTS: >100M. SourceCurrent:tlO nA typical. 2100modules comprise a multi-channel sysTheSeries AMPLIFIER: adjustable.ten channelsin 5. . 2 pV p-p at 0.lc). to Configuration:Two-to seven-wire half-.four 2l20A Conditioner/ Amplifierc. 2.i. Range:0. Independentlyvariableand regulatedexcitationfor eachchannel(0. Fully adjustable calibrated gain from I to 2100.loomAoutput. +m) detachablethree-wirecord. 2 5H x 2 . SIZE: 115 Vdc at l. Also ac input and dc outPutgo/no-go monitor. all regulatorscurrent-limited againstoverload. 7870efliciencyat full load.4 2150RACK ADAPTER APPLICATION: Fits standard 19-ir^(483-mm)electron\c €quipmentrack' and oneto AcceptsonePowerSUPPIY live StrainGageConditione$. to ascePtline cord from Receptacle adjacent2150RackAdapter.5 Vdc at 1.115. 12vdc trominal(9 to 18vdc range).17D in overall SIZE: .).25H x 19W x 14. 0 to 12Vdc (with switch)to readbridge excitation.6-m) three-wireline cord. ReversePolarityProtection:Internal shuntdiode. Relaysarepoweredby user-supplied voltage source.0 kg). Fuse:1A size3 AG (J2 x 6. Resistors: StandardFactory-Installed (174.and must be speci{ied whenorderingrack adaPtersor cabinets.25Hx2.50-60Hz.25H x2.2Aand +l?.214.l%) simulatet1000/.a kfl. WEIGHT: -4- 0 to 12Vdc (with switch)to readbridge excitation. 5. 5.OPERATEDPOWERSUPPLY OUTPUT: INPUT: METER: SIZE: WEIGHT: 2. l0-ft POWER: (3-zf extensionavailable. AcceptsonePowerSupplYand oneor two Strain GageConditioners.21bQ.4kd.6tb(3.).8KO f0. (133x 483x 360mm) 6." CALIBRATION: Controls:Two-position(centeroff) toggleswitch. Completelywired.80Din (141x 222x 350mm).3 2III DC.!€ at GF=2. 9 D SIZE: (133x 75x 279mm). . Power:40W typical. 6.34Din (133x 62 x j13 mm).0kd. Power60w max.5 216O adapterand DESCRIPTION: Completelyself-contained two or four wting for all cabinetwith channels.44W x 12. 3.5vdc at 1. tl5 Vdc at 1.1kd. l{EIGHT: PORTABLEENCLOSURE 2. 5.0tb(. }-fl (2.outputsare protectedagainst overload. dc outputgo/no-gomonitor' 5.2 2rl0A PowER SUPPLV(AC-OPERATED) OUTPUTS: INPUT: METER: SIZEI WEIGHT.55Hx8. 7 in 5 .230Vactl0% (selected internally).lA.75Wx13.7tb (3. 2. z-ft (0.44Wx12.0A and+17. 5.4mm dia. POWER: Fuse:lA size3 AG Q2 x 6 4 mm dia. OptionalCalibrationRelays:Provides remoteooerationof excitatios(off/on) and shuni calibration.l00W max.0A. 2. 107.2tbQ.34D in (l33x62x3ljmm). 9 4 W x 1 0 . WEIGHT: 2. (The andall Conditioners connected pilot lamp may take severalsecondsto extinguishwhenthepoweristurnedoff.-15.X20 andX200. The DC positionmouitorsa mixedoutput fromthe+15. . Primarily usedto adjust AMP ZERO and Bridge BALANCE.{MP ZERO Control A 25-turn trimmer used to set the electrical"Null" of the input amplifier zero. BRIDGE YOLTS Displays the voltage on each input bridge(asselectedby CHANNEL selecMeter tor)."A" simulates +1000p€.12a to extend range) EXCIT mustbe ON to setbridgebalance.A readinganywherein the bandfrom 9 to l1 on the Meterindi catesthat the input voltageis properfor the selectedtransformertap (see4.2 2120A STRAIN GAGE CONDITIONER (one channeldescribed.etc).thermalEMF from thebridge or ac pickupin the wiring. Other shunt calibrationconfigwations are possible by internal resistor and jumper changes(see5. Total amplifiergainis the productofthe multiplier switch and potentiometer settings.50to 12 Vdc. Mating connectorsupplied. As delivered. (Fully lit with 0.50.ard "8" simulates-1000p€by shuntingthe internal 350Ohalf bridge.(Any amplifier outputwith EXCIT at OFF is dc ampli fier offset.3.1e).) BALANCE Control A ten-turn potentiometerto adjust bridgebalance.The AC position (2ll0A only) monitors the p€ak-to-peakac line input (at a fixed transformertap). No readingindicatesthe equipmentis ungrounded.half and conn€ctinputgage(s). (EXCIT should be OFF and the input circuit connectedwhen this is done. Receptacle 2120AREARVIEW -5- . Also usedto monitor ac line and dc outputsof PowerSupply(seebelow).5Vpower suppliesand shouldalwaysreadoo the "DC" line at "10" on the Meter. POWER Switch The centralpowerswitchfor thissupply to it.0 CoNTROLS GAIN Controts 3.both identicaland independent). (See 4. full bridgescan be acceptedsimply by usingthe appropriatepins.) EXCIT Switch A toggleswitch controlling the excitation to the input bridge. EXTERNAL METER Jacks SuppliesMeter voltage to an external meterif desiredfor morepreciseadjustment of bddgesupplyvoltages.and+17. OUTPUT A three-pin connector delivels the amplifier output (il0V at tl00 rnA).) 3. Multiplier Switch:Providesgainstepsof X2.50to 10.)Mating connectorsupplied. The actual Conlrol settingis monitoredon theMeterandthe EXTERNAL METER jacks on the PowerSupply(theproperchannelmust be selected).Jcfor details. OUTPUTLamps LED indicators always monitoring amplifier output.07v output.Seey'.0 Shunt Cal' ibration). CIIANNEL Selector PositionsI to l0 selectchannelto display bridgeexcitationon Meter ("1" is channel farthestto left in cabinet. INPUT Receptacle (Rear Panel) A ten-pin quarter-turn connector to (Quarter.t 2tt0L/ztrr PowER SUPPLIES Potentiometer:Ten-turnwith counting knobprovidesmultiplierof0.) CAL Switch A two-position(with centeroff) toggle switch to shunt-calibratethe input bridge.Normalrangei2000ple. BRIDGE EXCIT A 25-turntrimmerto adjustbridgeexcitation from 0. Measurements withf l6 AWG (l'3-mmdia)' GroupP/N 12X300606) or larger. observe meterreadins: -6- 4. good ground. of course. turn the CHANNEL selectorto "DC". whereasthe voltageis actuallyI l5V. (Blank coversare availablefor unusedpositions. whichis not usedwhe-na 2l I I module is installed.AssurethattheoPeratingvoltageat the input connectorwillbemaintainedwithin9 to l8 vdc' asshownon Page7: Make connections . (2) distributcsdc regulatedConditionersand(3)connectsthebridgevoltagemonitoring meter in the Power Supply to the Yarious channels. 5.The utility receptacls 4.Eitherthe third pin wasno! used.otherwiseturn all POWERswitchesto OFF.Install SetPOWERswitchon thefrontPanel position of the the right-hand the 2lll modulein plug.lb Beforeinstalling a 2ll0A Power Supply modulein eachcabinetor rack adapter.Replacesidecover The POWER switchon the front panelshouldbe at OFF.with theexceptionofthe batteryopera12Vdc nominalinput.checkthat each2110A moduleis setfor the properac line voltage: Slide the right-handsidecoveralmostall the way back to exposethe two toggle switcheson the printed-circuitboard.one whilethe shouldbepluggedinto apoweracreceptacle. 4. or the receptacle If one or more 2150ten-channelRack Adaptersare used.1d Plugthelinecordhto an acreceptacle. 4. Installthe PowerSupplyin theright-handposition ofthe cabinet.2c l2 Vdc powerissuppliedthroughthefour-conductor maleconnectoron the2l l l rearpanel. Theaclinevoltageis signficantly below 1l5V (or 230V). turn the CHANNEL selectorto "AC".22 'fhe 2l I I rnoduleis capableof poweringup to eight channels(four Model 2120Amodules)at maximun ratedbridgevoltageand output currentor up to ten channelswben maximumbridgevoltageand output currert atenot required. all Positions 0. The metershouldread verynearthe lineat 10.lc Install2l20A Conditionersin theremainingpositions in the cabinet.1 SETUP AND AC POWER Readsloly(between8 and9-l/4).Pilot lamPlil Equipmentis not propedygrounded. usedis not properlygrounded.la The individual Conditioner and Power SupPly modulesare not stand-aloneinstruments.1g Checkbridgeexcitationregulators. Rack Adapter.Theredpilotlsmp shouldlight andthe metershouldreadb€tween9 and 11. securewith thumbscrews.e.Remole Power Supplyand resetinternalswitchfor LOW line' 4.from the ac receptacleof the cabinet.pushinto engagetheinput/outPut plug.a three-rxireextension cord may be required If more than one 2150 Rack Adapter is used.The2t 1l functionssimilarly to the 2110APowerSupply. it is suggestedthat the POWER be left on (for warrn-up).le Check ac power. On eachPower Supply.25in (133mm)'te*ical heightis requiredfor eachten channels.5and l2V.and setswitches(seer'.Ifit is Plannedto use the system immediately. NOTE: The fuseat the rearof eachRack AdaPter only fusesthe inPut to the Power Supply in that is not fused. grounded for best be ment must NOTE: If the line plug must be replacedwith a differenttype. On the Power SuPply.Scanthe CHANNEL switchthrough positionsi to l0. whichsuPPorts tion only.Turn poweroff immediately.) makingcertain 4.2 DC POWER 4. 4.ID).lh The systemis now readyfor use.lf Check dc power. This indicates that the internal switchesareprobablysetfor 230Vinput. 4. Reads0 (no reading)'Red pilot lamp not lit: The ac hasno poweror thefuse(at therear of the receptacle instrument)is open.This indicatesthat the inPut Yoltageis muchtoo high for the internal switchsettings(probablya 230Vinput 14'ith switchessetfor l15Y1.as marked. thisindicat€sthat either (l) ihereis an internalshortin oneofthe Conditioner modules(removethem one at a time).see4.Conlecessed nectionsare made to the mating femaleconnector (TRW/Cinch-JonesS-404-CCT. other Rack Adapters are Pluggedinto each othe! (using the utility recePtaclesat the rear) in any sequence. 4.Push the modulesin to €ngagethe power-input plugs. The equipgoes to a that the third Pin performance.sets for nominal I 15or 230V.. and the inPut/output push to engage cabinet. and securethe thumb screws.1b). Turn the POWER switchon(up). (Howshouldreadsomevoltagebetween to channelsnot coffesponding positions ever. Reads around 5.0 OPERATINGPROCEDURES 4. 4.observ€this color codewhenwiring the new plug: Brown: High line voltage Blue: Low line voltage(i.2b Rcmovethe line cord.theseshould be mountedin a standard lg-in (48j-mm) eqttipmentrack. and secur€the thumb screws.the othersetsfor NORM line (115/230Vllo7o) or LOW line (107l2l4Y t l07o).Ifnot.If not. remove module.switch installedwill.They are designedto pluginto aprewiredcabinetorrack adapterwhich(t) suppliesaclinepower(fused)to thePower voltagesto all Supply.wire.PegsrL full scale.readzero') 4.4Internal A diustnents)- 4. or (2) one or more of the regulatedpowersupplycircuitsis defective (see6. Oneswitch. to OFF. Tum POWER OFF."neutral" or common) Green/Yellow:Grouud If one2150RackAdapteris used. theremustbeaiumPerin theplug connecting PinsD of the internal the midpoirt this connects E. 1b: Input PIug Pin Arrangement 2l I I PowerInput Connections: plugs are desiredthey are availablefrom Measurements Group.INTERNAI- ro ro r-> r-- E E B aclrvE A2. ITT/CannonKPT06Bl2-l0P BendixPT06A-12-l0P(SR) 4.see theNoteon thefollowingpageand5. tors supplied. thus completingthe necessaryfull bridge for proper amplifieroPeration. there are used. Fig.To prevent powering any input circuits at this time.3 INPUT CONNECTIONS 4.la and lb. ro [-o (+E r<. Inc.3b Each channelusesa seParate plugs are suppliedwith each input plug. and 350O half bridgeto the $+ amplifierirput.|a: Input Circuits @@@ oo@@ @ @@ t-t <-- / Jumper rcquircd lar quadet ot hatl btidge. turn the EXCIT toggleswitchesOFF on all channels. E a ACflVE H020o) c(350o) F CI. (-) Negativesideof l2 Vdc source. respectivelY.no modificationsor jumpersare required of the exterinsidethe 2120AConditionerregardless (However. ( rz?z) Chassisground.If additional 21204 Conditioner -7 - NOTE: Exceptwhenusingan externalfull bridge.2d Turn POWER on and checkfor properoperationas describedin 4. power consumptionis negligible. Two loose (one per channel).) .1/ throughC. PREFERREO DUMMY A].TRANSOUCER 82.1rtfor the 2l 10A. (and interchangeable) 4.0 ShuntCalibra' lion.AI.usingthe connecwith Figs. or through electroric parts distributors.3a It is suggestedthat the systembe turn€d on and allowedto stabilizewhilepreparingthe input connectors. 4.NOTE:L€adsmarked"R" mustbe samelengthand sizelor bestbalanceand stability.Ifsystemis totally floating. EXTERNAIDUMMY QUARTERBRIDGE C2.GAGES BI. ' GrouP12X300515 Measurements (+) Positivesideof 12Vdc source. nal bridge configuration iuPuts provisionsfor accepting1000(}quarter-bddg€ and for changingthe shuntcalibrationcircuit .Connectto Systemground busor commontie Point.in accordance 4.3c Connectthe input to eachchannel.TERNATE FUtLBRIDGE H A L FB R I D G E Fig.connectto negativesideof 12Vdcsource. Generally. if the externalsignalis adequately grounded.11 ar. output plug' Two loose 4. b) Shieldsshouldbe groundedat one(and only one) end.calculatethe leadwire Ifexcescausedby the leadresistance' desensitiiation effective adjust required. b) IfPossible.ratherthatrthemore obvioustwo-wire circuit. to measuiestatic or dynamic addiFor precautions' of sets both observe required.A groundreturn existswithin the du€ to the presenceof the bridgestandard212-0.n is adequate.this cuEentwill flow through the input wiring to the groundreturn.a completelysymmetricalcircuit will yield lessnoise(e. 4.5 MILLryOLT INPUTS The2120AConditionercanaccePtlow-leveldcinputs. c) If lone leadsare involved. electricallyconnected d) Keepall wiring weUclearof magneticfields (shields do noi protect againstthem) such as transformers. a) In the quarter-bridgecircuit.Do not usethe at the accidentalgrounding) usecoaxialcable (that not is.group all leadwiresto the samcchannel in a'bundle to minimiz" temperaturedifferentials betrxeenleads. 880f.Iligh sourceimpedances offset impedancethe ableoffsets(with a 5000Osource RTI).pleaseconsult GroupTechNoteTN-501.a half bridgeon or near the specimenwill usuallyshowlessnoisethan a true quarter-bridgecoNection)' -8- b) Theinput cannotbecompletelyfloating..For this mode.relaysand beavypowerwiring.or all three'asbestsuitsthe situation' 4. whichmusiexist. normally the shield is grounded at the INPUT (andinsulatedagainst connectorandleft disconnected gage end. tio.this ret. do shieldasa ionductor wire).With a floatinginput (in whichcase the balanceresistormust remain installed).6 OUTPUT CONNECTIONS CAUTION: If it is possiblein any wayto damagethe to the OUTPUTwith indicatoror recorderconnected shouldnot be the OUTPUT mA.01% VishayResistor SolderPad (ComponentSide) Static Data: Precisesymmetryin leadwireresistancejs in hiehlv desirableto minimizethe effectsof changes aribient temperatureon leadwires.this noiseis usuallyrelated to the 50 or 50 Hz line power in the area: a) Always use t$'isted multi-conductor wire (never parallelconductorwire).al or within the 2120A. acculacy data sivein view of gage resisor increase wire size. increase factor.the l20O dummy terminal(pin H of inPut Plug)is converted to a 1000r) duomy termiral by removing a shunt from a factory-installedVishay 880Oprecision resistot in serieswith the intemal l20O dummy gage' To make this conversionthe user must desoldera solderpadlocatedon thecircuitsideof the PC board' Fizurei showsthelocationofthe 880fIresistor(compo-nentside)andthe solderPad.with serial numbers above 85000.see4''24)' The useris also cautionedregardingtwo sourcesof error: possiblysig:nificant a) Biascurrent:Eachinput (pinsA andD) requiresan innutcurrentofapproximately10nA.dependingon whetberthe may be botb if data. naee iaice .shieldedwire is greadypreferred. .th€remrlst be a sroundreturn(generallylessthan l0 MO).al informationon elecuicalnoise.4 WIRINGCONSIDERATIONS affectwiring techCertainimportant considerations purpose ofthe testis nioue. either exte. provide the caPability for lO00Oquarter-bridgeoPeration. e) With long leadwires. this resistancecan be removed (removejumPersP andN . a t\{o-conductor as c) The specimenor test structure (if metal) should be to a goodground.}t0.the bias reouiredat pin D will flow directlyfrom tbe balance resistor. motors.In the caseof thermocouolesweldedto anominallygroundedstructure.NoiseCon' Measwements trol in Strain GageMeaswements. although it may prove unnecessarym some casesusingshort leads. may apProach0.6a Eachchannelusesa seParate Conditioner(one 2120A each with plugsaresupptied desiredthey are plugs are additional If oerlhannetj. (using pins A and D). alvays usethe threeleadwirecircuit shownin Fig' 14.withlow sourceimpedanceLtlisis insimificant and canbe offsetwith the AMP ZERO canresultin measurconirol. 4.d4. provided two requirements are observed: a) The common-modevoltage should not exceed tl0V in normal operation'and Eust neverexceeda peakvoltageof *25V. .NOTE: 21204 Strain GageConditioner.2 mV b) Anv nonsymmetryin the ground returnsof the inputs-willreiuce the CMR of the amplifierto some degree. or 140 15V of inDuts until the channelshavebeenbalanced(see connected 4.bui the biasfor pin A witl flow throughthe entireinput circuit. DynamicData:It is extremelyimportantto milimize thi electricalnoisethat thegagesandleadwirespick up frorn the test environment.g.E' balancecircuit' However.12). 8b Magneticallydampedgalvanometers.7 I+U (Eq. or readily availablefrom Measurements throughelectronicpartsdistributors: -"--- .8a Fluid-damped galvanometersare most frequently andsimple useddueto their high frequencyresponse A seriesresistoris matchingnetwork requirements.normally6 2A +5%)' The desiredvalueof R34 and R37 can be calculated with the followingformula: R7n RSHUNT 5 RcALvx.the denominatorin the fractionis 1.typically severaltimes the "mAi inch" speci{icationof the galvonometerratherthan the maximumsafecurrent' This will establish rhe minimumvaluefor Rsruxr.if the output is to be fed into a high whichhas impedancedevice(suchasan oscilloscope) only a singleinput pin (plusgound). 4.With a load of l00O or lower.The mountedasR38on seriesresistorismostconveniently the2120Apc board(first openthe shortingjumperon thepc boardpadZ). is zero (within 7 mV maximumcircuit offse0.but do Dotusea valuebelowl5O._ (Eq.However. of the galvanom€te!. any betweenpins that thisdevicebeconnected other connectionmay causecrosstalkbetweenchannels.the shuntresistormay b€ omitted.if no shunt resistoris used (Rsnum= oo).R37).' Ro^"" Rsturr OUTPUT LIMITS The output is capableof +lOV into a load of l00O or higher. this inputcanbe connectedto pin 3 of the OUTPUT plug with little error (typically 1 mV referredto the output) due to crosstalkbetweenchannels. lMAx: maximumcufientoutput in mA. Inc. alwaysdesirableandashuntresistormustbeprovided currelt in most casesto keepthe peakgalvanometer belowthe 140mA outDutof the2120. The seriesresistorvalueis nevercritical.++.6b Threepins are providedfor eachchannel: 3 -----J5- 'r OUTPUT 2 --]-}- OUTPUTCOMI/ON 1 --J SHIELD (CHASSISGROUNO) If the "maximum safecuffent" ofthe galvanometeris lessthan 140 mA.6c It shouldbe notedthat the OUTPUTindicatorlamps on the front of the 2120Aat all times monitor the voltagebetweenpins3 atrd2 ofthe OUTPUTreceptathe outPutvoltage cie. Theshuntresistorcanbelocated on the pc boardasR39. require series 4. l) where: Rcr=currentlimit resistorin ohms(R34. Full bdllianceofeitherlampindicatesa voltageinexcessof 70 mV (possiblyashigh as l5V).it is advisable.but for lse. any value with\n!2570 of the abovesolutionis adequate.3) Rseeres3 '. TheoriginalsolutionofEq.Ifboth lampsareextinguished. Pin 2 is output common. but in ro case greaterthan 140mA.Group. In the aboveequation. proper dynamic achieve to resistors "damping" networkis usuallyrequired: A three-resistor response.8 GALYANOMETER MATCHING 4.now calculatethe seriesresistor: 5000 T- no^tu (Eq. RcALv= input imPedance If the maximumsafecurrentis 140mA or higher.but with low-level outPut signals. Measurements Group 12X300556 Cinch-JonesP-303-CCT-L 4. 2) JSAFE wherc:lsere= maximumsafecurrent(mA). calculated. -9- where:m.4. 4. The maximumoutput can readily be limited to less than 140mA by increasingthe valueof two resistors per channel(R34and R37. the output will deliver up to tl00 mA.4rsis the milliamperesrequiredthroughthe galvanometer for thedesiredfull-scaledeflection. 3 and2.) Having choseDa value for the shunt resistor. calculate the shunt resistor: It is generallynot essentialthat the output leadsbe shietded. .of coursea differential input (usingpins 3 and 2) is preferred.2yielded the maximumvalue.Ifthe OUTPUT is connectedto a low impeit is essential dancedevice(suchas a galvanometer). 4.which is connectedat one (in thecabinetor rackadapter point to cbassis-ground harness). (A moreco4servative solutionformostgalvanometErs below2 kHz would be to recalculate with a response the above.Thus thereis a rather largerange but neverexceedthevalueoriginally ofvaluesacceptable.rsuse lhe maximumrequired operatingcurrent . the OUTPUT low-resistance 140 mA for at this time. at bestnull.ll range between1000f}and 25 000O. Rorup is the specifieddanpi:rg resistancefor the galvanometer. 4.l.notethat thisis the systemvoltage dampedsystems (includingthe dampingresistor).12 BRIDGE BALANCE 4.9e Turn theCHANNEL selectorto DC. on the leftmost channel.turn the EXCIT swiich to ONI then tum the BALANCE control to extinguishthe OUTPUT lamPs' 4.4 lViring Consid' eraliotr for furtherdiscussion. 4. (if the "+" lamp is etc') lit. tum the POWER switchon.9 OPERATION 4.setthe CHANNEL selectorat AC. If.TOEXCITATION 4. 4) where:. 4. pleaseconsult MeasurementsGrouP Tech Note TN-502. An alternatesolution is: D------- 50 x l0l - (Eq.84.adjusteachAMP ZERO until both OUTPUT lampsareoff. this is an indication noise(probably50 or 60 Hz) at the input' ofexcessive Checkwire shielding.connectan externalmeterto the EXTERNAL METER bananajacks on the Power Supply (the minus jack is nominally chassis-ground). 4. 4.4rs (Rs.notjust the voltage acrossthe galvanometer.9c On the Power Supply module.l2aAdjustbalance. -10- RANGE ]UMPERN RANGE]UMPERP IIr--.in ohms.For eachchannel. 5) m vFS where:ztZrs is the millivolts requiied for "damped syst€ms"for the desiredfull-scaledeflection. both lampsarelit. the meter should read within the AC band. adjust BRIDGE EXCIT (using a small to readthe desiredBRIDGE VOLTS on screwdriver) the PowerSuPPIYMeter. (Eq.Referto 4. Turn CHANNEL selectorto channel2 andrepeatthe aboveprocedureadjustingBRIDGE EXCIT on the next channe!continueuntil all installedchannelsare satisfactorilYadjusted.9b Ifit is possibleto damageor overloadtheindicatorsor ro theOUTPUTSwith l5 Vdc(or recorders "oonected devices). Rcelv istheinputimPedalceof thegalvanometer. any value Values within t2570 ofthe abovesolutionis adequate.4rs is the rnicroamperesrequired though the galvanometer for thedesiredfuIl-scaledeflection. Optimizing StrainGageExcitation lzvels' 4. it is desirableto usethe maximumexcitation that the input to eachchannelcan accept' gagesor gagesbondedto a Smallor low-resistance poor thermal conductor(suchas most plasticsor use low excitation' composites)must necessarily For idditional informationon excitationselection.Note that in the abovecircuit the galvanometeris protectedby the maximumvoltage(tl5v) from the 2t20a.10aSet desired excitation on each channel tum the CIIANNEL selectorto channel l.{1Y + ftPaMt.The 10r}shuntresistorhasbeenselected on are based formulas the following arbitrarily and this value. NOTE: To achievebeststabilityandlowestnoiseat the output. wi. plugsshouldnot be connected 4.i t---_-l -t r--lt T =l -l LEFT CHANNEL =1 T II II T FTI= l T I LJ ---l rll : -: RIGHT CHANNEL RIGHT RANCE IUMPERP RANGE IUMPERN .lobConnectthe gage INPUT plugs (if not already connected). The seriesresistorvalueis nevercritical.the metershould readon the DC checkline.Irswill always be above lather 150O. 4. Rsrnres= 50x 105 P. turn the adjustmentcounterclockwise.9d On the PowerSupply(2110Aonly)module.11 AMPLIFIER ZERO Adiust the AMP ZERO for eachchannel'(To some is affectedby symmetryof extint theamplifierbalance seenby the amPlifierinputs') the sourceimpedances Using a small screwdriver. the 140mA iurrent limit is neverapproached becausethe value of Rser. Most specificationchartsfor magreticallydampcd galvanometerslist data in mY l\n (mVl cm) fot . etc.9a On each channel make certain that the EXCIT switchesareOFF (thusremovingexcitationto all gage circuits)andthe CALswitchesarein thecenter(OFF) position. The series resistor and shunt resistor are most conveniently mountedasdescribedat the endof 4. If greateraccuracyis desiredthan can be achieved wiih the built-inmeter. The red Pilot lamp shouldlight. For example.25 mV).assumethat the desiredoutput is 25-mm deflectioo on a recorderfor a 500p. In practice. Howevet just before taking data. jumpers can be located at both area P and N. Fufther assumethat the desired output from the 2120A.for example.a 50-mm deflectionshouldoccur when the 1000&€shuntcalibration resistorin the 2120. and should be doneoccasiooallyon an extendedtest.Bridge balance may be disabledby removingboth P and N jumpers. .it is highly desirableto document the output noise attdbutableto wiring and other sourcesvs.13c Once the GAIN and BALANCE contrcl settingshave been finalized. with a l20O full bridge. This is especiallynoticeablefor stain gages with resistancesof 3500 and higher. First therc may be a very small offsec(5-10 mV) beMeen true zero outPuland the zero indicated by the lamps and.f) full bridge.lt - Beforetaking dynamicdata. if the OUTPUT lamps arenot at null (both extinguished)adjustAMP ZERO as This can be done at any time during a testnecessary. and the multiplier switch at X200. half or 350.5 pV per pr. 4.pleaseconsultMeasurements Tech Note TN-50 | . A recunent waveform indiofthis frequency) (usually50 or 60 Hz or multiPles wiring gages in the to the pickup at the or electrical cates gages:if excessive.the sourceshouldbe locatedand corrective measurestaken. b) Under no-loadconditions(and with CAL at OFF ard EXCIT at ON) the OUTPUT lampsshouldindicalenull. ffoi. it is recommendedthat the knobs be locked in positio[ to prevent accidental rotation.einput.Set the GAIN control at 8. An extensionof the balancerangewill producea reduction in the setability of ihe balance con[ol. Using shunt calibration (such as the 1000t!€ built into the 2120. the balancerange will be reducedfor lower bridge resistanceand increasedfor higher resistances. Spare or unusedjumpers can be storedon the Pins next to the right channelgain switch.e = 1.13b All controls arc now set. the balance range is reduced to under t700p€. thus doubling the balance range. .even though the mathematicalapproachis possible in many situations.veCotltrcl itr Straitt Gage Measureuents. 4. if not. For additional intbrmation Croup on eleclrical noise.{ is selected(assumingGF=2. the total dynamicoutput which includesthis noiseplus the dynamicstrainsignals: Momentarily tum EXCIT to OFF.it is advisableto checkbalanceson eachchannel: a) Briefly turn EXCIT to OFF. With full bridge inputs other thafl 3500.€per volt ofexcitation) andbridge excitationhasbeenset at 5 Vdc. second.12b Connect OUTPUT plugs for each channel (unless alreadyconnected). At 500p€ the bridge will deliver 1. 4. Any outPutobserved now is NOT causedby strain (whethera dynamicstain is beinggeneratedor not). "White" noise(full spectrum) is due to the amplifier and cannotbe rcducedexceptby rcducing GAIN . NOTE: In both stepsabove.25 mV (500ire x 5V x 0.it may be necessaryto compensatefot a small mechanicalor electricalzero offset in the recordingdevice.13a Adjust GAIN for each channel. the BALANCE conFols can conect for approximatelyt20009. If the balance range proves inadequatefor the gagesor tlansduce$ in use. assumethe input is one activegagewith GF=2 (this will produce0. For example. 4.e unbalaacein a quarter.25mV = 1600).5 ttYN/p. To achieve2V output from the amplifier will requirea gain of 1600(2Vl1. for which the calibrationresistorsare calculated). is 2V for 500tr€. NOTE: As delivered.13 GAIN 4.00. The knob can be unlockedsimply by rotatingthe lever back to the counterclockwisestop.0 Shunt Calibrstion.4Conditioner).See5.ler gairt required.The user is cautionedto considerthe effectsof leadwire resistanceand the calibrationcircuit aclually in use when calculating the stmin simulatedby shunt calibration. 4. adjust the BALANCE controt. the shunt-calibration m€thod should also be used as the final exact adjustment.14 NOISE b) Ernpirical: Without rcgard to bridge excitation or amplifier output voltage.it may be desirableto observethe outputrecordermther thanthe OUTPUI lamps. Also.adjustthe GAIN asrequiredto achievethe desireddeflection. the "balancelimit resistol' can be changed from 75 000O to 37 000O by moving the jumper from areasP to areaN.it should not exceedseveralmicrovolts rms refered to the input (that is. Countingknobs utilize a lever which must fust be pulled arvc-vfrom the panel and then rotated clockwise (towards the bottom of the panel). the observedsignal divided by amplifier gain).There are two general methodsof settingthe GAIN control: a) Mathematical:In many casesit is possibleto predict and preset the amplif. thus tripling the original balanceEnge. 90 (20 ft AwG 26.i . (use 7 in Eq.To properlyshunt-calibrat€ 5.ly0'2Vo' Use:Quarterandhalfbridge(full bridgewith reduced accuracy).tpted technique ".a good approxrmatlon (whichassumes the pot is at mid position)is: p.t. 3.25 m. 6 Ri is resistanceof K= K' dummyresistor.30 (t ft AwG 26.. of strainSage(ohms)' Rc : resistance in serieswith of leadwire(s) RL = resistance of activegage(usuallythe resistance (ohms). (ohms)' of calibrationresistor RCAL:resistance K maybe the actualpackagegagefactor of the strain gug. 0'8mm dia) For 350Ogages: 0. 0. = of ba. and 5' (Note that resistorsareusedfor CAL A and CAL B. op. in ur".lance Potentiometer' . 85ft AwG 20) i6 m. voltage-sensing remote a onlY theerrorthusintroreni(to thecalibrationresistor).' = Re (Rr + 4RsL) (Eq.this correctionis or.3 SHUNTING INTERNAL DUMMY GAGE (120 or 350O): Use:QuarterbridgeonlY.iOg.4 ^^ dia. signal one reasonis that curcarnes now lead. fourtimesthatwhichwouldbe ducedis approximately expected"bynormal "leadwire desensitization" equatrons.While the exactvaluedependson the positionof the balancepotentiometer. ?I20A Conditioner).Simulatestensiononly' Locationof resistorsandjumperson the printedcircuit boatd is shown in Fig.3()).No specialwiring rcquired'Can simulate tensiotrand/or comPression' maybesignifLeadwiredesensitization Disadvantage: 6)' Eq. oneleadwire) Whenshuntingeitherbridgearmto whichthebalance it is theoreticallynecessary limit resistoris connected.4mm dia. As a rough guide. 5.6) where:u€cAL: strainsimulated(microstrain)' of arm R'a = preciseeffectiveresistance shunted(ohms).rr.the sameequationapplies: pec^L= Ri r( (Rc.4 SHUNTING ACTIVE GAGES Whilethereis no electdcalproblemin shuntingactive qaeesal the specimen(they must be accessible)' with only the iciomplistringthis at the Conditioner sedous will introduce usual ihreeleadconnection The resistance' measurable have errorsifthe leadwires be to is supposed which lead.1 EQUATIONS by shuntinganyone Shuntcalibrationcanbeachieved ofthe four armsofthe input bridge(whichincludesan active gage(s)and the bridge completionresistors within ih. so seDarate maybedifferentvalues.ages applications.4a -' isto providetwo additional u.30ft Awc 20) i2.The 2120Aprovides for shuntinganyof thesearms'No matter wbich arm is shunted.to calculatestrainuse these th.l ^.t Ri = 349.170error will be introducedif the of eachleadis: resistance For l20Ogages: 0.ift. effect in determining shunting this for to correct R'r.. 8) 2p^+fts+4Rer of resistoror where:RA = resislance gagern arm. &' = effectivegagefactor of strain gage. 0'8mm dia) activegagesor transduc.9 m. Rp resistance of balancelimit resistor' RBL= resistance It shouldbe notedthat.for quarterL. leais dedicatedto the calibrationcircuit. for the 2120AConditioneras shipped(whereshuntcalibrationis acrossthe 350O dummy half bridge). or it may be adjustedfor leadwire desensitization: K=K=+= ^c where: (Eq. + Rir) x 106 (Eq.t"tion this is customarilycalledthe "fiveleadwirecircuit".ttuio or the characteristics _ 5. and in no way doesit verify the ability of thegageitselfto meaof its performance' . The aboveproblemappliesequallyto active(or comandto all transducer instressanalysis pensating). 5. icant Locationof resistorsandjumperson the Printedcircuit board is shownin Figs. of activegage Adyantages:Sameresistorsregardless resistanci. .?) r JiL 1( = packagegagefactor of activegage. Automaticallycorrectsfor IeadwiredeAdvantaqe: (usingthree-wirecircuit) No specialwirsensitization gagereslstance' of precise independent ing.0 SHUNT CALIBRATION that the Purposeof NOTE: It shouldbe emphasized shuntcalibrationis to diterminethe performanceof the circuitinto which the gage(s)is wired.Accuracy Disadvantage:Only usableif intemal dummy gages arein use.- INTERNALHALF BRIDGE SHUNTING (350o): 5.o. 0. 4. $"{. 3: CAL on Internal Ealt Brfulge(Tensionand Compression) \a/ IH!ii... l iilfi. i[1 iL_l? /K3 CALA & B: Tension(+) o l-.'.: ^ H3-i. @ Fig.$'{'{ l*itl.fu^Iilf 9 f'l P-..*tt I ntiitii.*.*.- fi) IHL_lil..[ l. 1: CAL on Internsl HaA Bridge (Tension) .1=:-:.$.".+i i-] l'T'[i"*.REM E CHANNEI T +il+i l$"[.r. (x) Fig.3 c-1 P.1 3- .'[ T lril'--r{ I ::: LJ I i ii!.lt666 r- nrm I i*l'T:{t t-li )il ? l---: " *fi3rJ" CHANNEL CALA: Tension(+) (-) CAL B: Compression NOTE:Thisis standardconfiguration of the 21204as shipped...i o ]. l P-.J ?:---i ^ H3".o i#.. 6: CAL on Dummy Rxistor -14- CALA & B: Tension(+) .- (x) IHL-lll$r^lit' ...l=:-:-: +ilFr I l K3 lrfrtr..*.. *'.-". 5: CAL on Internal EaA Bridge (ComPression) (x) +! i-l u'T't$..REM o d T Tijt"[i'i." /rfrrr.{l::: r-'r o |..+r-ri-l u'T'll"*...:-[ -. IEL-JL **-'.i:ulvnJ..*." (x) Fig..3=:...J ililili t$"{. *'*-' o'" o K3 a ooooo o.'*.i id..*.- B )Flill$'T?{t _.^r# 1....{ T 1.{T. o (-) CALA & B: Compression )r..x€M ." o (x) Fig. I qrTi i^:.{:::l n P-.. P+ o. ' ^/a. 7: CAL on Active Gage(Tension or Compression) SOLDERPADT IS CTOSED(FARSIDE) ^\dT e"t r- r5i-l B tl (x) i..3_l CHANNEL trilt:.8 )r I li l:--) ' No vacantpin available.l.T REM nil*#. 6lo i E/. H.X1 PADT ls ct-osEo(FARslDE) Fig. or F.{I I 69?e69 K3 ! ll e6ad A ililill .Nfl' n ntiltii.l'r/ al P-. Hemove existingwireandusePinG. 8: CAL on Active Gage(Tensionand Comptession) -15- .REM B T ! li il3.{ T ln.$"1"$ YY a 66 ?9 ooo dd \J RIGHT CHANNEL P.4+t1 IHL_lr eY9 .SOTDER PADSS & T ARECLOSED(FARSIDE) CALA&B: (-) Compression A let a ]Elii.ffi$ CHANNEL o tl (x) lAl PADSS&T ARE CTOSED(FARSIDE) SOLOER CALA&B: Tension(+) B Fig. CALA: Tension(+) (-) CALB: Compression -.1.l tf CHANNEL o K3 ililli :$"1'$'1. 001339 120401330 90 ldA 75 mA 50 rnA 2 1 5 00 l 2 1 6 0 AS MOOIIIEO FOR REA4OT' OPERATION 2120a AMPUFI€R(5) While the relaysarenot installedunlesssPecifiedat the time of order.aPPlies.PinsJ and K on the inPut connectorareusedfor this Figures7 andEshowa halfbridge.) 5.ibration for true quarterbridges.butthe aDDlication.r( = K' (In a transducer.Fig' 7. sion onlY.orderrelay 2^120A from Table5.theconnectionshould bemadeat theconnectoron thetransducer'. 9.Remote-operalion Rack Model2150 bility mustalsobe specifiedfor th€ The sysEnclosure' 2160 Portable Adapteror Model Fig. also appliesto full bridgesand wiring cal. kit sel€cted 5.1. in as shown wired be tem would -16- Fig.OPERATION RELAYS Four isolated relays can be provided to operatethe followingfunctionsin tbe 21204: Shunt Calibration (A and B) Bridge Excitation off (to checkamplifier zeroor electricalnoise) Table 5. 9: Remote'OPerationWiring. comprestransducers. directly The addedexternalleadsshouldbeconnected to the strain gageterminals.CHANNEL MODIJLf.Ri would be the effective resistanceof the shunted transducer arm. they can be easilyinstalledlater by a oualified techniciaq all wiring already exists in the module'For after-saleinstallation. PART NUMBER 120{01338 120.5a An externaldc powersupplyis requiredto controlthe caparelaysin the 2120Amodules.1 OPTION I) Y24 OPERATINC VOLTAGE 5V t2v 24v REQUIRED FOR CURRENT TWO. Ri = actual gageresistance. .5 OPTIONAL REMOTE. However.PNP (Motorola. affect overall Performalce: a) Shunt-calibration dircuit.int€rnal adjustmentproceduresand schematic diagrams. MPS8598) Q3 14x200184 Transistor.OP01CP) U5 r4x700096 Amplifier (PMI. Bridge Volts ]. LM337LZ) 12X3005s6 Regulator (National.NPN (MotorolaTIP-3055) Symbol MI P/N U1. Diodesdnd Rectifiers: D'iode.OPI5EZ) U6 l4x700ll8 Amplifier (PMI.Rectifier Motorola 1N4004) Transistors: Transistor. l6.2110APOWERSUPPLY 6. Power InPut M1 200-130583 DC-DC Convefter z1 26X100190 DC-DC Converter 22 26X100191 Meter. to some extent. LM723CN) Diodesand Rectif.U3 14X700040 200-130s83 cR1-CR17 14X400135 cRl S 14X400088 Q1-Q3 t4x200t9l POWERSI]PPLY 2111DC.BridgeVolts IntegrotedCircuits: Regulator (National.3 FIELD. Bandpass can be increased to 50 kHz by removing jumper R.1 CUSTOMERMODtr'ICATIONS There are three simple modifrcations that can be made to suit specific measuremeotrequiremelts.Zener13V (Motorola. c) Changebandpass:As shippedthe 2120A is config' ured for a bandpassof 15 kHz (-3. Transisto(NPN (Motorola.OPOTDP) u7 14x700087 It is rccommendedthat a defectivemodule be retumedto the Measurements Group for repair and recalibration in order to preserve the factory warranty.0) cRl 14x500108 Trsnsistors: Transistor. b) Changebridge BALANCE range:See4.REPLACEABLE COMPONENTS Diode. user organizationswith qualified electronic techniciansand suitable calibration facilities may choose to repair the units by refening to circuit descriptions. At the €xPimtion of factory waranty.IN4743) cR2-CR5 14x500107 . Consult Measurements Group Applications Engineering DePartment for assistance.en: Diode.9-z) extension cables are available to operatethe modulesoutsidethe rack or enclosure: 15-pin(for 2120A)PAI200-130596 25-pit (for 2110N2111)P/N 200-130597 6. it should be noted that these modifications may. LM723CN) 14X700153 u2 14X700040 Amplifier (PW OV21EZ) U3.Refercnce (National.2 SERYICING 2120ASTRAINGAGECONDITIONER InputPlug 12X300515 OutputPlug IntegratedCircuits: Regulator (National.OPERATED 12X300606 Coflnector.Rectifier (Motolola1N4002) Diode.0 Slruzt Cdlibrction. MJE52l) Ql 14x200189 The componentson the following list are thosewhich may be required in the repair of a defective amplifier Other componentsmay be obtainedfrom the Measurements Group by referenceto the schematicdesignation and the serial number of the amplifier.To facilitate service. LM3362-5.0 dB). See5.NPN (Motorola.PNP (Motorola.124.0 SERVICING DATA Description 6.U4 t4x't00162 Amplifier (PMr.. Sparejumpers may be stored on pios next to gain switch.3-ft (0.MPS8099) Q2 14X200183 Transistor. Meter.MJE37l) Q4 14x200i90 Individual schematicsof the vadousmodulesare included on the following pages. 4 INTERNALADJUSTMENTS If equipment malfunction occurs during the warranty period. SetGainPotentiometer PlaceDVM probesacrossC5. to 10. Adj ust R I 6 for outPutvoltageof + 17. S.lD) SetEXCITswitchto OFF. deflection.5 SCIIEMATICS diagramsfor the 2il0A PowerSupply'2l1l Schematic D C . The following adjustment Procedures are intended to aid the technician in the proper adjustment of the ampl. Switch power to ON. SetGainMultiplierto X2. Set front-panelAMP ZERO control R20 8 turnsclockposition. Repeatprocedurefor both left and right channels. to X10.(See4. Adjust Ri 1 for outPut voltage of -l5Y xlVo Adjustment Common-Mode PlaceDVM plobesacrossC14.an inPut connectorwith S+.Zero Adjustments 6.5v tl 70. wisefromfull counterclockwise of zeroai00 PV. AdjustR21for minimumoscilloscope 60 Hz deflectionshouldbe lessthan7 mV Adjust R6 for outputof +17. Adjust R29for readingof zero*1 mV. Switch power to ON. -18- 6. Place DVN{ probes acrossC 11. BothBALANCELED'sshouldbe extinguished. MoveDVM ftom TPI to Pin 3 of outPutconnector. 6.4b 2111DC-Operated Supply Adiustment from(S+. ConnectDVM from TPt to Pin 2 of outputconnector (t2). Adjust R6 for output voltageof+15V tl7o. tl5V outputsare fixed bY design. PlaceDVM ProbesacrossC12.5V tlEa6.S-) to Gndon Apply60 Hz. NOTE: Allow 30'minute warm-up before making final adiustments.4c 2120A Amplilier Adiustnents Ulless otherwisespecified. DVM reading for R13 Adjust SetGainMultipl.ierto X2' AdjustR23for DVM readingof zerot1 00 ptV Checkandadjustzerosof R13andR23until thereis no zeroshift whenswitchingbetweengainrangesof X2 andX200.ifier in the event that compolents are changed during tloubleshooting and repair of the unit subsequent to the warranty Pedod. Enclosure . 10Vp-p sinewave inputconnector.50 SetGainMultiplierto X200 andPotentiometer (Gain= 2100).and Gnd terminals shorted together must be con[ected to the amplifier input for all the following tests.5. 6.O p e r a t eP d o w e rS u p p l y .4a 21104 Power Supply Adiustrnents Set line voltage switch to corresPondwith operating voltage. the defective unit should be retumed to the MeasurementsGrouP in order to Preservethe factory warranty. arefoundon thePagesthatfollow. 2 1 2 0 AS t r a i nG a g e 2150 RackAdapterandthe 2160Portable Conditioner. to Pins 3 and 2 of the output Connectoscilloscope connector. l FA <p< >qa9 ETF UE tho o trj = *tE riN\ 'z'd/ F 9-o i6r i ljE n >6 li E. !iqEc :t9d q E ?3 . 6 gEE6 ooci. E3 = € .: :: * pE€t .o = |\ c o F z !. E :E ! veEZ I:. eis z- d yiEi i I fi E i1 eE dE :r:-: . b. €I P E iEaE E !J-L : oaEi ri ' 'c e a= 2n o o i.: .1 = ut t. Ea 6 {! : o.=. t r= + 3 -t9- ..E E q .E:i F E g.eeeE i i . 95 LE E o c.-----------..^--- "1 5l(-' EFIF E' o* 4. :a"o JE. .z U z9 o0h FT 6\\ = at. UI = I T !tt 6>\ 'iE!/ 1 < . F z = ul i].E.=E IiE. E a.o . EE .Je EEEz 9E+E !6FE m u1 6^ E] * g2 Y tqgL .t aii !dE re gE Ef. e E' 4 d i. sEe'& tr3E 3 . .. js 5: gEiE E Ee eE€€ t E.94 E E l i o . 'SE€I t 5."zE.l-.E E-. SE€5 'I 3l L ff I t t.--1 aE. .4ig..92 e ri9 E PNI aE t t 6 e ! t . g __5_i-_'_ lrh Ira a \i i Rc :gi..6 i II II ---Er E cls ! slq tut El lil 1 I g EIP2 s|E t 4i Tlt Il llllc llliJ. zit "i Efl. ! 9 . u v i. E4g Ei4 A"iE. G.. i i\E:u sils:P$H 8-.^ 2 at F 2 |rl ".i?g EHUiT F TA E+\\ tEil t 00 e. EF=: '- 2E i.E. I aa! | :!i I eE d"E rF3? $i !i .ii6 = tu z F e6 Ez <o< >9R EEF o < cho z at !J = Eti 3"^itF.9 FE'HS -2t - .o = d E iE tel EJ. .i!. E9 5 € Ei4.. 9Eo * rtE ri "".. =.l .:G19i . I E ei Eee. !6FEc l4E. Je atE? irl ril s :E*r ay l* .{ t ti"r -E a.9 !t lr 2 I 4ut er= o ul Fract E?Y HA E < i" r'r . €EEE :.ct \c = e a4.E!i* E 92A E 9-e o : a . qE d o . q FJ : J l .xH <i l 44'.et!€ E _ : -* !4 .E. EE . l '' . . o ul E t 9i 9Y 9r $ t3 l t. 3 4 U 4 4 l- o L i z i i .l I fr 7 9 t 7 o iz 'C t-F ] lE) \ 0. 5 '9E€I i b.E .gI i 9 q n E ll6 I t-l F l x .e- .!!i. \ ( 6 t !!. FEFc ITE.C. a5 an <Fi E F z <! oO ''-. iE+A . c i s !qo: E . tEl lJ ' l4l lsl tt.i as ! N !30E h:d: :5E5 tt) U] 0l uiL Nl S r o o ^^c6 tae2 eE 2 a . 5I 3 k H'{ Yt . (! 2 $ o o 9 l3l rNt iFi l€l le. ic> 6 t n I 9-o i 7J . or at our option. fhis warranty shall not apply to any instument that hasbeen: Group itl such a manneras to injure.Oran authorizedrePat station.includine anv implied face.or conclusions put arecomPletelyin thehandsofthe The mannerin which theequipmentrs employedandtheuseto whichthe dataandtestresultsmaybe in anyof its products' to det'ects incidental or consequential pu.specified t"pf""" #y insuumenttharfails to i" . and buyei in"fJi !oo* pui"ftased fro."-"nts c"oop.conditions.rg name of another company.""t .loss o1time..hereof'Purchaseracknowledges the for a particular purpose.understanding.expressedor implied.andbuyer'ssoleremedies. to prop"ity.Iimitarions. theperformaoce..adjusted.to therepalrOrreplacement shipmeol prepaidby thebuyir.Inc' insbumentsundelwarranty$ ill be prepaidby Measurements chargesof rcpairedor replacement Retumtransportation of anytestresults' no responsibilityofan! fb[m for theaccuracyor adequacy andassumes Groupis solelya manufacturer The Measurements which mayresultfrom the useof its equipment.'. warrantiesof merchantabilityor fitness This warranty is in lieu ofany other warranties.we will repair.Ourlries. da!a. tO be ex-amination.is limited under this and factory wolkmanin materials goods defects free ftom of to the delivery iterns is limited consuma'ble and similar rechaEeablebarteries ship. any of our ploductsfoundto be defective At no charge. ing from personalinjurY..excluiions liability against or asserted claim any Groupharmlessfrom herebyagreesto indemnifyandhold Measurements buyer..r""hased'as is.i.a.and the Purchaser ro so noiify suchbuyer This provisionis not intendedto afford by the'failureOf the Purchaser imoosedon Me$uremenrsCroupoccasioned underthelaw' Purchasers t"'fr"q*nf p*ahot"" anywarrantiesor rightsnot expresslygrantedto suchsubsequent at any time.limitedlo thePurchase Croup.anties which e*tenttbeyondthe deicription onsalesBan' agent. and disclaimeri of rhc warrantyprovisions. installed..*" prior thJtime to staied herein.laritems.ty loss of profits or income. or accident.worked on or alteredby personsunauthorizedby the Measuremenrs stability'or reliabilityof theinstrument: juigment..fr" ij""iiir.p"ir Croup' lnc andbearing by Measurements "ralg"'uUf.ty . in our sole i) reDaired..including t'ut not limited to ".ssoleliabilities. betweenthemanufachrrer thefull undelstanding This wanantyconstitutes by an authorizedofficial of and signed writing in made unless hereaftei be binding hereoi shall terms vary the or purportingto modity Croup.Measurem".ndsimi.iold in conjunctionwith equipmentmanufacrured The warranly on nonshipment' of y"* the date aftef warranty !o one "iur-.. for consumerproducts'so theabovelimitations damages some statesdo not allow the exclusionor limitationof ilcidental o! consequential or exclusionsmay not aPPIYto You. iamages for loss of use. upOn that any instrumeot Of solediscretion. or loss result' a"-"g".or usedotherwisethanin accordance iii) connected. Measurements -23 - . ii) subjectedto misuse."menr.or al our shallbe. Group for notifyinganyslbsequentbuyerof goodsmanufacturedtyMeasulements is responsible The purchaseragreesthatthe Purchaser put"hased by such any t::l!o-o-d:.rp "..t" Cro.lnc.There are no war.underthis agreement The Measurements retumed tOour fadOry' when defective. within theapplicableperiodof time from thedateof original transportation Group.-i.Inc."f" of "onthe part of Meas.withoutincurofits instruments the right to makeanychangesin thedesigno! construction Groupreserves The Measuremenrs prcviously delivercd' in uoits whatever change ring anyobligationto makeany price.negligence.Group. employeeor other that no states p.. OT with theinsffuctionsfumishedby us.at our plant..and agrees MeasurementsGroup. aamales for irrjrrry to the person."haserMeasu." any liability in connection person has made any such representations or lnarrantiei or otherwise assumedior MeasureEents Group any-breachof contract or of out arising have may buyer toaives all rights gooasto itre po"ctr"s"" foye" tt"t"ty i"iifrin" .of after within three perform as.WARRANTY and factory workmanship.. warrantsall instrumentsit manufacturesro be free from defectin materials Coverageofcomputers'calllshipment years date.".r. proves.rePlace under this warnnty. to any inciilintal oi consequentialdamages.Inc. shailin no way be liablefor damages or agreement andbuyet andno terms. Shain GageConditioner channelsto beusedin the displaymode. Power SupPlY. COMMON MODE COMPLIANCE tl00 mV (rear-panelinput) minimum. STORAGE STABILITY t3 counts/minutemaximumat +750F(+230C). I channel. 2 tb (0. i1999 counts. Theseunits simplyslideinto eitherthe 2150Rack AdaPteror the 2160 Encloiure. 2 5H x 2 . COMMON MODE INPUT RANGE input). tl0V (X10range).An additionalline connectionis no. ATTENUATOR ACCURACY t0.An externalmonitorthe2130anddifferential to canalsobe connected ing device.0/6 t5 countsfor repetitivesinewaveof frequencylessthan 1000Hz. t10V (rear-panel ACCURACY StepInput: t0.0570 or better.0516reading+0.2/s*5 counts for repetitivestepinputsofgreaterthan 500usecduration. indicagive simultaneous connectorto output rear-panel the input.l% or better. X|.front-panel jacksareprovidedforutility inputssuchasmeasuringbridge ixcitation via the 2ll0A or 2lll EXTERNAL METER on jacks. . SPECIFICATIONS nominalor typicalat +23oCunlessnoted.The fronhpanelEXTERNAL input is single-sided on the2131.BNC (rear panel). INPUT IMPEDANCE 100Ko.suchasan oscilloscope..9 7 D i n (133x 75x 279mm). All specilications 2130/ 2131 COMMON SPECIFICATIO NS INPUT CAPACITY 10 channels. andMIN (usuallynegative) PEAK RESET Manualor Automatic.The 2130/2131will acceptandswitchupto teninputs. channelsel€ctorin a 2100System-compatible 2131 also includespeak reading capability.l/6 t5 countsfor step input of greaterthan l0 milliseconds duration.Additionally.:--r required2 PulseDuration RepetitiveSineWaveInput: 45. S I Z E& W E I G H T 5 . SWITCHED OUTPUT Not attenuated. tionsfor a giveuselected INPUT YOLTAGE RANGE t1999 mV (Xl range). INPUT IMPEDANCE Greaterthan I MO. DIGITAL DISPLAY 3-l/2 digitLED.\Vo X5 countsfor repetitivesine waveinput of frequencylessthan 200Hz. ACCURACY full scale) t(0. PEAK MODES MAX (usuallypositive)excuffion excursion.APPENDIX MODEL 2130DIGITAL READOUT AND MODEL 2131PEAK READING DIGITAL READOUT GENERAL 2130SPECIFICATTONS The 2130moduleprovidesan LED digital displayplus a The Package.6mm).3 tn (7. requiredas ooweris derivedfrom the 2110Aor 2ll1 PowerSupPly ihroughtherackadapterorenclosure. UPDATE RATE nominal. DISPLAY IIEIGHT 0.BNC (rear Panel). POWER 2ll0Al2lll 2131SPECIFICATIONS INPUT VOLTAGE RANGE ti999 mV (Xl range). RepetitiveStepInput:10. 9 4 W x 1 0 . tl9 990mV (Xl0 range).Standardcables(two signalconnectionbetweenthe supplied)makethenecessary 2l1Ot2l3l and eachof the 2120A. 3 readings/second.Numberof steps -> l0 milliseconds _^^. bananajacks (front parel).8 kg). The mosi negative(alSebraic) input is stored. Automatic reset will everY5 to l0 occur aPProximatelY seconds. MIN .5 vdc Power supply. oneof the rack or enclosure . BNC receptacleusedto monitor the input signalon an externalindicating instrument such as an oscilloscope.The mostpositive(algebraic) input is stored. The EXTERNAL positionselectsthe to the adjacent input that is connected front-paneljacks.2130/2131REARVIEW (typ.0 OperatingProcedwesithe 2130l2l3l is installedin exactlythe samemannerasthe 2120AConditioners'filling slots. I I SETUP asdiscussed Install the 2130/213I into therackor enclosure in 4. to 2120. Typically used to monitor strain or bridgevoltage.position I i s c h a n n e lf a r t h e s tt o t h e l e f t i n rack. MAX . typically bddge voltagefrom 2tr0 Al 2rtl EXTERNAL METER jacks ATTEN Switch Xl positiongivest2 volt range. MAN (Push-buttonSwitch). display readsthe existinginPutlevel.4. the storedpeak reading (213f) ' is periodicallyresetto the existing input level.(Cenerally.etc. connected Inout Connectors l0 BNC receptacles (RearPanel) OUTPUT receptacles). The desiredchannelis selectedwith the front-pauel CHANNEL selector switch.The pilot lamp LED indicates whenpoweris on.When off (down).When Pressed.When set to AUTO. POWER Switch SIG OUT (RearPanel) PEAK MODE (2131) Switches This switchesthe 17.resetsPeakreadingto the existinginPut level. EXTERNAL Jacks Provideability to accepta front-panel input.) RESET Switch€s AUTO (ToggleSwitch) .the button should be held 1 secondor more fot a com' Pletereset. ''- ON-Display readsthe stored peak reading. Xl0 position givest20 volt range (tlOv for 2131). CHANNEL Selector PositionsI to l0 selectthe input channel for display. CONTROLS OUTPUT DISPLAY Providesa digital readingof the input as selectedby CHANNEL selector. SetPEAK MODE rotary switchto MAX andthe roggleswitchto ON.the readingvr'ouldhave beenan unchanged+1500in the MIN mode or +1700in the MAX mode. There is an internal adjustmentin the 2130/2131for span sensitivity.a cable can be made asd iscussedh 4.the2130/2l3l readsdirectlyin millivolts(tensof millivoltsin theXl0 mode). .0 OperatingProcedures 213012131.A five-minutewarmup is recommended. to Setthe2l3l PEAK MODE andRESET-AUTOswitches off. NON.Observethe OUTPUT DISPLAY whenadjustingthe2120Abalanceandgain the controlsaswell aswhentaking data. NOTES In both MAX and MIN modes. the display will read slightly higher in peak reading mode becausethe pickup appearsto the 2l3l as a normal (althoughsmall) dynamic signal. To usethe 2l3l without utilizingthe peakreadingfeature. set PEAK MODE rotary switch accordingly arld repeat prior two steps. A very slow display changecan be due to Peak storage drift that is not necessarilydue to changein the strain amplitude. Replacement parts cafl be obtained from the factory.if RESET resultsin a +1500court reading(staticload offset). . If desired. . T u r n P O W E Ro n t o b o t ht h e2 1 1 0 A / 2 1I Ia n d2 1 3 02/ 1 3 1 . turn PEAK MODE to MIN If the MIN peakis of interest. .10utilizing the CHANNEL selectorto choosethe desiredchannelfor display. OPERATION To preventdamageto small gagesorsensitivegalvanometers. r ReadOUTPUTDISPLAY. algebraically subtract the MIN reading from the MAX reading.900Vto the input arldadjustingthe potentiometerat rear of meteruntil readoutdisplaysa1900. o PressRESET-MAN firmly (apProximately I second)or wait for automatic resetto resetdisplay. preferably using the standard cables. Xl mode.achieve paragraphsandproceedasfollowsdependingupontypeof input signal: RECURRING PEAKS . MAX or MIN should now be displayed according to the position of the PEAK MODE control. SetRESET-AUTOto off (downposition). . a Load specimenor structurethroughthe peak valueof interest. 200-130827. Establish static load (if required) and cyclic load.9e. o Set PEAK MODE to ON.accessory2130'A27).a -440 A-3 .INPUT CONNECTIONS Connectthe OUTPUT connectorofeach 2120Achannelto be displayedto the appropriate2130/2l3l input. lf necessary. bridge voltage can be displayed by connecting bananaplugjumpersbetweenthe 2l l0A/21 I 1 EXTERNAL METER jacks and the 2130| 213I EXTERNAL jacks (connect red to red and black to black).6a and4. Switch RESET to AUTO. To read the oppositepeak. If insteadth€ excursionwere +200.For example. connectthe 2120AOUTPUT (pin 3) to the centerBNC pin and the shield (pin 2) to the BNC shell. andpressRESET-MAN again.RECURRING PEAKS . whereas MIN peak storage tends to drift in the positive direction. . beforeturning on power to the 21l0Ai2lll and completeall stepsin 4.a peak readingcan haYe eithera positiveor negativesign. Typicallythe MAX peak storagecan drift in either direction. Io the presenceof 50/60 Hz pickup.6b. count input excursion from the offset level will result in a readingof+ I060 in the MIN modeor an unchangedreading of +1500in the MAX mode. throughy'. Tbis can be ttimmed by applying exactly t 1. Ser PEAK MODE toggleswrtchto off (down position). A decreased cyclic strain amplitude will be reflected h the display after resetoccurs' SERVICE A schematicof the 2130and the 2l3l can be found on the next page. For convenience. o To determine the peak-to-peak amplitude. this pickup should be minimized by using twistedand shieldedstrain gageinput wiring. engineering The AfiEN switchis normallyusedin the Xl positionbut theX10positionis requiredwhenlhe readinggoesover1999 In the countsandthedisplayflashes(indicatingoYerrange). OUTPUT DISPLAY may be set up to readdirectlyin units. keepthe PEAK MODE and RESETtoggleswitchessetto the off (down) position.To take peak rcadingsusingthe in the above calibrationasdiscussed desired 2131. Therefore. Continueon y'. r PressRESET-MANfirmly (approximately I second).two of which are provided (MeasurementsGroup No. lNc. as the bssisfor minufacture or saleof such item.4nd shall oot be rbe propirty of Measuremlnts .frema.rty of Measurements . in whole or in part.ap.They arc' an{ 1ta]. MEASUREMENTS SCHEMATIC 213IPEAK READING DIGITAL READOUT .and shallremajn tion orrepairoftheitems reprcsented. SCHEMATIC 2I3ODIGITAL READOUT 200-r30826C NOtESI W Tlese drawings and specificatiottsarc intended to provide information foi the proPerutilizationor mailtenancc orcalibration or rcpair of the items reptesented. and shall not be lhe prop. Inc.tn Group. F|'JF uelsunEMENTS The6e drawings and specificationsare intended to provide information foi theproptrutilization or maintelanceol calibraTheJ arc..F6qEFr 6 F'rrPUr I ID1SFLAYI cRoup. Group.ep-duced-o" copied. copied.in whole or in part. lnc. as rhe basis for manufaclureor saleof such ilem 300-045251G L-A GROUP'INC.odu""d'o. 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