The subiecl of qn elecfrolytic copocitor's ESR hos generqted <rlot of interesf in recent issues.Alon Witlcox hos tqken it o stoge further in designing o procticol ESRmeler. This firsf porf deols wirh the operotion of fhe circuitry used in fhe meter . 'uh''E$ Design.,of M6tBr VCR ot monitor. A TV display may be pulled in from the sideVtop/bottom.Diode and transistor failure can occur over a period of time. These and many other problems are often causedby capacitors, with normal capacit'nce but high ESR, which does not exist as a static quantity and therefore cannot be measuredusing a conventionalcapacitance meter or a:DC ohmmeter.ESR exists onlv when alternating current is appliedto a cdpacitorbr when a capacitor's dielebtric chargeis changingstate.It can be consideredas the total in-phaseAC resistance ofa capacitor, and includesthe DC resistance the leads,the DC of resistance ofthe connCction the dielectric,the capacto itor plate resistanceand the in-phaseAC resistanc-e of :.,' ESR the dielectric'material at a panitular frequency (my ' In view of Martin's 'r review and also the articlesby Ray italics) and temperature. ,' , . Porteron a capacitor'sESR (Januaryand April 1993)I The componentcombinationthat constitutes ESR can won't say a lot aboutESR here: it would simply be rep- be thoughtofds a resistorin serieswith a capacitor:the etition. To put it in a nutshell,a capacitor'smeasured resistor does not exist as a physical entity, so a direct ESR (in ohms) is an indicationof its 'goodness'. The measurement acrossthe,'ESRresistor,is not possible. Iower the ohms reading, the better the capacitor. An If, however, a method of correcting for the elfects of ESRcheckcan give an early indicationofcapacitor fail- capacitive reactanceis provided, aid consideringthat ure, and is far more useful than a capacitance measure- all resistances in phase,the ESR can be calculated are ment. Indeed many faulty electrolyticsshow OK when and measured using the basic electronicsformula E = I checkedwith a conventionalcapacitance x R! This is the basisof the designof the Capacitor meter. In recent months I've talked to many people who Wizard." don't appreciate importanceof ESR and in what the sense differsfrom capacitance. I feel it worthwhile Design Criterio it So including an extract from a technicalbulletin on the Capacitor manufacturers quoteESR valuesmeasured at Capacitor Wizard writtenby Doug Jones, President l00kHz. So this is the test frequencyI chose.The the of Independence Electronics Inc. It sums up the ques- impedance inductorsin the microhenries of regioncan tion of ESR well. be measured this frequency,enabljngthe c-ondition at "ESR is the dynamicpure --as they w6ar and the gap resistance a capacitorto of video heads be gauged of to an AC signal.High ESR can causetime-constant prob- deteriorates, their inductance falls. lems,capacitor heating, circuit loading,total failureetc. The Wizard has a buzzerthat soundswhen the ESR powersupplymay not startreliably- or is below lCl or so. A capacitorwith an ESR of less A switch-mode start at all. Slight hum bars appearin the video of a than about lC) is generallyconsidered be good, so to lot has appeared recent issueson the subject in of the ESR (equivalentseriesresistance)of an electrolytic capacitor. The Capacitor Wizard was reviewed by Martin Pickering in June 1998. It's ' designedto measurea capacitor'sESR in-circuit while ignoring any componentsthat are connectedto it. The. unit described'in this. artible performs the same task, .. and a lot of work has been put into achieving the end ' result. Even if you don't get around to building the meter, this article will give you insight into the design criteria and the way in which the instrumentworks. But build it if you can: it's effective, very useful and inexpensive. ri 'i r16 M a r c h 1 9 9 9T E L E V I S I O N :I . "=;;-;r;9,;:, .:. ,i:;ril r. ;; ,. .::,1 it .j ,. . :..:.: . \ I digress.To get back to the point, the opa amp usually:requires positiveand a negativesupply are with respectto a common earth. These.supplies often noi shown on circuit diagrams, being taken for granted.Thq common earth (0V line) servesas a refereirce point for the voltages that are presentin the circuit and as a'return path to the power supply for any currentsgeneratedby the device's operation. The main point here is that if the voltageat the + input with respectto the voltage at the - input, the increases if output voltage will be positive-going.Co,nversely the with respectto the voltvoliage at the + input decreases hge at the 1 input the output voltage will be negativeto going.Thus in normal practicethe outputcorresponds the difference between the inputs. If the op-amp doesn't have any negative feedback and the + input is at only 0'lmV abovethe - input, the output voltage will be close to that of the positive supThe Op-Amp ply rail. If the + input is lower than the - input by the The circuit'uses the basic opamp as an oscillator, sameamount,the output voltagewill be close to that of amplifier;' dslsctor, voltage-follower and .'comparator. the negitive supply rail. Thus the gain is equal to the So'it's appropriate devotesomespaceto a description' average slope, which is typically l0V/0'1mV = to of the op-amp and its associatedcircuitry. Incidentally 100,Q00. This very sensitiveproperty is used in comthe term'opcrational amplifier' relates to its use in ana- parat<ircircuits (it's'used in the ESR meter's buzzei logue computersand appearedin a paper by Ragaziuini circuit). But the op-amp is far more useful when.the and others in 1947.The first general-purpose op-amp, output is restricted to narrower limits. with.differential inputs and using the familiar triangular symbol'for circuit rcprcsentation,was :introduced;in. The Precision Inverting Amplifier ' 1952r 6Model K2-W, by'.George A. Philbrook This is one cif the'riiost common opimpapplications Re.searches Inc.). It's sobering to think that almost forty and is usedin the secondand third stagesof the meter. yearsago an early op-amp, the P2, cost $227 - an eighth' Circuit operation will hopefully be made clear by the of the cost of a VW Beetle at that time: now a superior rather unusudl representation(due to Tom Hornack) device can tie bought for less than a pound. shownin Fig. l. The op-amp is a high-gain (x100,000 or so) amplifiAt (a) the op-amp is arranged to provide a voltage er that usually has two 'inputs, on-e non-inverting gain of two. The fact that in this case the output is Qabelled +) and the other inverting (labelled !). For inverted (the gain'is.minus two) is not important. The practical'purposes.the gain.rcan be considered as heavy negative.feedback,viaresistor forces the outRf infinitely high, with no cuirent flow at the inputs. The put to be such that the voltage at the - input is equal to opamp'isr,designed primarily to' operate stably'with that at the + input rjvhichis'oV. Remember that the ophcarlr- nefative. feedback' In 'fact from 'the' hisfelisal:; ::amp responds' the"difrerencebetween its' inputs. As td poiriio"f:vlcw:de opamp andithe concept of negative' ;,point X is at earth'potential, there is "lV across Rin' feddb4k(the, invention :of fi,S.'r Blach-'workingrforr' 'Ohm's .and,ther,cirrrdnt flow via Rin, calculated by ,(lk0) Bell_'[5t*iratories, in 1927) are synon5rmous. Law;.iS lmA. jTherc is no current flow at the Black' wa5''w6ikihg'on telephones,' tis bu;ective biing to:. input of the op-amii So this lmA flows via Rf (2k0) achieve'stable gain independent of the characteristics': whiih thus has 2V'across it. of a valve (a thennionically-activated FET to youpgNotice how Rf and Rin behave like a seesaw as the sterSl). When he tried to patent his negative-feedback input goes from a positive to a negative value, with the amplifier in 1928-the idea:was ridiculed. Over the piVot at the null point X. This point is referred to as a years however this concept has become one of the virtual earth. There is no current path between point X most important in the field of electronics. Marconi had and earth, and point X is always at zero voltage with much the sameproblem. It seemsthat people often dis- respectto earth. miss things they don't understand. The concept of a virtual earth is used as a short-cut this is a very useful feature in situations where you waht to cheik a number of suspectcomponents,. it means that you need refer to the meter ohly when there's no beep.I've incorporatedthis facility, b'utyou' must bear in mind that a lot of the capacitorsin which we'ire interestedhave ESR values of less than 0.5C) when good. More on this later. I'd like to stress this basicpoint before going any furthen as with the CapacitorWizard, the meter described in this article doein't measure a capacitor's microfarads. It simply lets you know if the capacitor is or isn't up to thejob. After gaining somepractical experience with the meter, you will soon get to know"what reading to expect from a good capacitor - taking into accountits capacitance and voltage rating. But in'any casethe readingobtainedwith a faulty capacitorusuallf lea1e1little doubt as to its condition. ' 'Anyway, (ol {bt DSUd Fig. 1: Precision inverting op-amp circuit, ia) witn a positive input, (b) with a negative input. Note how Rf and Rin behave like a seesawas the input goes from positive to negative, with the pivot at the null (virtual earthl point X. The gain of the stage is RflRin, so the output is Vin x Rfl&in. TELEVISION March 1999 317 ESR METER # The Oscillqtor - History At the heart of the meter there's a Wien bridge network oscillator.This form of oscillator has an interestinghistory which is worth a few paragraphs. In 1939 William RedingtonHewlett (co-founderof producedhis StanfordthesisA New Hewlett-Packard) TypeResistance CapacityOscillator.It madeuseof a resonant network that had beenconceived Max RC by Wien (pronounced Vene) in 1891. The American inventor Lee DeForest(yes,we can blame him) hadn't started the ball rolling yet with the creation,in I 906, of the triode valve.So therehad in I 89I beenno meansof obtaining electronicamplificationand Max couldn't have got his network to oscillate. That wouldn't hav'etroubledhim, as he was using the network for AC bridge measurement. Amazing what people got up to over 100 years ago, isn't it? I think it was, once again, somethingto do with telephones. But Hewlett had the pentodevalve at his disposal. He also had Harold S. Black's pioneering work on negative feedbackto assisthim. In addition there was Nyquist's Regenerative;Theory,which described the conditions necessary oscillation. for. Hewlett showed that the Wien network could be made to oscillater A crucial problem had to be resolved however, that of stage glin. With a gain of less than unity there would be no oscillation. With a gain of greater than unity there would be distortion. With unity gain there,will be what Hewlett wanted, a ,sinewave. He had a flash'of inspiration; the solution 'was literally staring him in the fate - the electric light bulb. : Hewlett's oscillator.wasa two-valve affair, with a 6J7 as the oscillator and a 6F6 as the output stage.His solution for gain stability was to wire a tungstenbulb between the cathode of the 6J7 and earth. The negative feedback was applied between the anode of the output valve back to the cathodeof the triode oscillator valve. If the output increasesfor any reason, so does the current flowing through the bulb. As it warrns up, its resistance increases. doesthe level of So negative feedback, thereby stabilising the oscillator's output. Hewlett's idea of employinga light bulb was brilliant in its simplicity. It survived in the Hp200 series audio oscillator during a fifty-year production run - into the mid Eighties. About fifty years after Hewlett built his oscillator Jim Williams, who was working for Linear Technology Corporation, was sitting in his den one rainy Sunday trying to think of something to do. His old HP200 caught his eye. Peering into the back, he saw the light bulb where it had beenplaced half a century ago, and wondered how Hewlett's oscillator would perform using a modernop-amp. He went on to knock one up - the original circuit is shown in Fig. 2 - and was pleasedto find that it had a distortionfigure of only 0.0025pei cent. Perhapshe could improve on it, by eliminating the bulb? Jim was the first to use a JFET in place of the bulb, but with this devicethe distortionfigure roseto a massive 0.15 per cent. Unfortunately there's not spaceto explain why the use of a JFET gives such inferior resultscomparedto a bulb. In the event Jim discardedthe JFET in favour of an optically-driven CdS photocell.This, in conjunctionwith five op-amps etc., producedan analyser-limited distortionfigure of 0'0003 per cent (threepartsper million). At one point during his questJim writes (AnalogueCircuit Design, Butterworth-Heinemann)"I could almost hear Hewlett's little light bulb, which worked so well, Fig.2: Jim Williams'original circuit, the firct attempt at combining an op-amp with a Wien bridge network to form an oscillator. 656t1 Fig. 3: An op-amp Wien bridge oscillator arrangement with the output set at 6V p-p (positive peak shownl. At the resonant frequency points a, b and c are in phaseand the waveforms at the op-amp's inpuF are a third of that at its outpttt. The ratio BflRin = 2. when the operation of a current-to-voltage converter is analysed.From Fig. I you can see that, becauseof the virtual earth,Rf appearsto be in parallel with RL. So the voltage acrossRf appearsacrossthe load as the output voltage. But although the null point is cortsidered to be at earth potential, at a microvolt level it's very much active. It can be seenfrom Fig. I that the stagegain, within the limitations of trhe supply, is determined by the ratio of Rf to Rin. Incidentally there's a frequency limit on the gain: with common types of op-amp we are limited to a gain of about x10 at 100kHz.If the resistorsin Fig. I are transposedthe stagegain will be 0.5 - the circuit actsas an attenuator. Overview Before we go further, it would be as well to provide a quick introductionto the meter circuit presented here (seeFig. 5). The first stageconsistsofa l00kHz oscillator, whoseoutput is fed to the capacitorbeing tested. Put simply, the currentflow throughthe capacitor is sensedthen amplified as a voltage. It's finally detected and measured the meter movement. by The better the capacitor,the lower its ESR and the higher the meterindication.It's not quite this simple, because meter must ignore the other components the connected the capacitorbeing tested. to We'll come to the solution to this problem later. i. :l "!t ''{ 318 M a r c h 1 9 9 9T E L E V I S I O N # ;ffi ,.* *; ,i$ +if 'i{ii;r-." ::; for laughingat me". So no apologies the useof a light bulb'in this design- Operotion of the Oscillofor Fig. 3 shows the Wien,bridge netwoik oscillator as you probablywon't haveseenit drawn before.It.illustrates the situation at the peak of the positive-going half cycle. The positivefeedbacknetwork consistsof the series-parallel (lead;lag) network: the negative RC feedbackloop consistsof the presetRf and'bulb Rin. We'll consider the RC network first. At very high frequencies shunt capacitorin the lower arm of the the bridge will appearto be a short-circuit and there will be no signal at the op-amp's + input. At very low frequenciesthe seriescapacitor will appear to be opencircuit and again there will be no input from the feedback network. At somepoint in between there will be maximum output from the network. The frequency at which this occursis equal to ll(2nRC), which is called the resonantfrequency (fr) of the bridge network. At ' this point there is no phaseshift acrossthe bridge, and the upper arm of the network has twice the impedance of the lower arm, giving a transmissionlgss of 1/3. To overcomethis loss and achievethe required stagegain of unity, the closed-loopvoltage gain (ACL), which is set by thc ratio of Rf to Rin, must be three. The formula for the closed-loop gain of a non-inverting amplifieris ACL = M/Rin + 1, so Rf/Rin must be two in order for ACL to equal three. , .... At power up the negative feedback is low, because the bulb is at its lowest resistance,and.the gain is high. As,a rcsult oscillation begins immediately, aud ' the bulb is warmed by the current current flow. Within a fraction of a second the resultant increase in its resistancereducesthe oscillator's output. It settles at the level at which the bulb's resistanceis half that of the feedbackresistor Rf. So the value.of Rf sets the that the bulb's thermal amplitude,of ,the"output.,Note delay means that it cannot follow oscillations at relatively high frequencies.It.responds to the RMS.cur. rent,gnly, and phuslehavps,F a.nordinary resistor. . i ;g . - - b r ' . , i ] ; , t . r , f'+ ' The Bulb ,: i . ,.'..+,jr,y ',j: " Yflt - 0v Vioa -lY D5UO Fig. 1: Pr*ision rectifier circuit, (al with positive input, bl with negative input. In (aJ the op-amp's orrtPttt goas as low as required to overcome the forward voltage drop acrosli D'| and still satisfy Ohm's law as far as Bf and R|n are concerned. D2.is off as the voltage at its anode is 2'6V le*s than that at iE cathode. In (b) D.l is off, its cathode voftage being 0'6V higher than its anode voltage. The conduction of D2 limits the positive o,ftptlt 8t 0.6V. This limiting factor speeds up the recovery of the op'amp when the input goes positive again. measured the resistauce of pulbs that I thought might be'iuitable, and found that the cold resistance of a 28Y,24r.A hulb is l70Q-. fitis soemedto be about right. When I tried it -,bingo! So when, in this connection, you see "any low-voltage, 50mA or so bulb" you can in future read "a28Y,24mA bulb". The oscillator,will work a treat. The final stageof the basic meteruses an op-amp as a precision rectifier..Keeping to the type ofrepresentation we've used before, Fig. 4 shows its method of operation. With a conventional rectifier there's the drawback that the signal must rise above the diode's forwardvoltage drop before conduction begins. This can be overcomeby the use of an op-amp in the circuit. At (a) in Fig. 4 the input is positive and the output reduces the voltage at the cathode of Dl. This enables the input to carry on via Rf to the amplifier's output. As in the caseof the inverting amplifier circuit, the output is again Vin x Rf/Rin. The diode's forward voltage drop, which is 0.6V with a silicon diode, is overthe come because op-amp'soutput goeslower by this amount,satisfyingOhm's law as far as Rf and Rin are concerned. Point X is still held at earth potential by feedback action from the output. D2 is off at this time, as the voltage at its anode is lower than that at its cathode. When the input goes negative however, as shown at I ; :'r.;l ;: : i. .'' .:'. {" . ' Although the Wien bridge oscillator is the accepted statrdard'at frequencies up to say lMHz, the use of a bulb for gain control, popular in the USA, has never found favour on this side of the Atlantic. I think I. know thc rcason for this., In most textbooks things begin to get a bit vague iwhen it comes to the actual type of light bulb to use. It is often said that any low-yoltage, low-current bulb can be used. This is not so. I have seenthe following flawed reasoningin some books. Take a l2V, 50mA bulb-which has a resistanceof l2Vl50mA = 240Q. The feedback resistor must be twice this, i.e. 480Q or a lk() preset. There's nothing wrong with this value for the feedbackresistor, but it won't work with such a bulb. The point that's been missedis this: the bulb must be operatedat a current level that gives a large changeof resistance. This occurs when the current is only a few mil-. What liamperes,and nowherenearbulb incandescence. we requireis a bulb that hasa resistance about 200f1 of when cold. When the type of bulb normally specifiedis used, the result is overloading of the op-amp, distortion, heavycurrentdrain and dependence the supply on voltage for regulation rather than correct bulb operation. I didn't do what Hewlett did, which was to plot the 1/ characteristics variousbulbs carefully. I simply of The PrbcisionRectifier March 1999 TELEVISION 319 ESRMbTER $ iq Fig. 5: The basic meter circuit. VBI sets the oscillator's output level. Pin 8 of tCl and tC2 is connected to the +ve suppty, pin 1 to the -ve supply. (b), the op-amp's output rises to the point at, which D2 conducts. The current then flows via Rin, point X andD2. DI is now off and the output ib zero.- Bosic Meter Gircuit The circuit of the meter itself is shown in Fig. 5. The Wien bridge oscillator, redrawn, is the same except for the inclusion of a lf,l resistor (R3) between the bulb and the 0V line. Depending,onVRI's setting, the bulb's current ii typically 3.5m4 RMS.'As a resriit, in the absence of a capacitor under test about lOmV peak-to-peakat lOOkHzis developedacrossR3. " ' ' VRI sets the amplitude of the oscillator's ouq)ut. In this case the butput is used only for feedback,ind is set at 5V feak+o-peak; There is nothing magical about this figure, and with this application no test equipment is required to set it. It's just that'to get a higher level output you would have to use a higher supply voltage. In fact however the higher thb output voltage the better.' The ESR of the'capacitor being tested forms part of a potential divider with thez.lQ resistorR4. The voltage waveform across this resistor, as a result of the current in the capacitor, is amplified by the rest of the meter circuit. Bear in mind thit with the range of ESR values we are measuring an ideal mid-scale figure would be about 3Q. With low. ESR'value'C(good capacitor) the signal across R4 is high, while with a poor capacitor it wlll be low - often, in relation to 2.7d2,there can be an effective open-circuit. Now if, for example, the ESR is 2.7Q, half the sourcevoltagri acrossR3 would be passedto the meter and a half-scale reading would be expected.It doesn't quite work out like. this however, becausethe source voltage is not independentof the lohd, and we will be setting full-scale deflection with R3 and R4 in parallel (test leadsshorted). If the ESR tends to go below the value of R4, it becomes more effective in increasing the voltage acrossR4. As the ESR rises abovethe value of R4, it becomesless effective at incrEasingthe voltage across R4. Hence the non-linear scale,which is ideal with this application.R3 and R4 are of necessitylow in value, becausethey compare with the values of ESR in which we are interested..Thebonus here is that because their low valuesthi effect of associated of incircuit components becomes insignificant. The design of this littlernetwork is such that the waveforms across R3 and R4,are virtually in-phase regardless ofthe value ofthe test capacitor.So we are measuringthe total in-phase AC resistanceto which Doug Jonesrefers (seequotation earlier). You might wonder why the test.signal amflitude is so small. It isn't becauserfe warit tg avoid turning on semiconductordevices - we could go up to a'coiple of hundred millivolts before there'would-be:any worries about thit, It's'similly'i"mattef .bf power con-r sumption. Even our tittle iOmV requires 3.5mA, irnd in this caseI have (dare I claim cleverly?) useda current source thdt's already there. A l00mV test source would require a hefty 35mA, quirc a drain on resources.If anything the value of the lQ resistor could be even lower, so that with respoectto2.7Qit would more closely approximate a constant-voltage source. You may think that to test an electrolytic capacitor effectively a fair old currentishould be pumped through it. Not so. A healthy l,Q00trrF capacitor will still present0.05C1 so to a couple of':millivolts and or ' :1 thus be producea reading. The signal across R4 passesthrough two stagesof amplification each with a gain of ten, and is then detected for the meter movement. There is furtheri amplification in the detector stage.The output iS integated by C4 to produce a DC output of about l.3V with the test leads shorted - this correspondsto zero . . r : ' E S R . , i : The basic meter circuit usestwo dual op-amps.you' will seethat the signal path from the oscillatoi in ICI passes IC2 then back again.fhil is done to prevent to the first, sensitive stage of amplification picking up a strong oscillator signal in the samepackage. .l ii \i ,+ ,.1. The Power Supply There is no need for a regulatedsupply, because the bulb stabilises oscillatorand the implification facthe tor of the op-ampsis fixed by the ratio of the feedback and input resistors. usedis shownin Fig. _Thepower supply arrangement 6. IC3a generatessplit rails from a single supply line. The voltage at its output pin 7 is at half thC iupply voltage,because the voltage ar its - input (pin 6) is equal'to the half-voltagelevel set by R[2 and Rl3 at its + input-(pin 5). This way of using an op-ampis' known as the voltage-follower. There is total negaiive feedback, and the c-losed-loop gain is unity. 320 March 1999 TELEVISION _-;.,1,i, - i r ' : ;:. i: i?t ESRMETER - R1( 55k 22 ol oa Fig. 6: The..iplit-rail generator and buzzer comPdrator circuits' is The meter's total current requirement is only some output froin the meter rectifier circuit, across C4, of mA for the on indicator D6- appiiea to the + input (pin 3) for comparison with the l0mA,.plus a ,couple pin 3 Two PF3 batteries in..series are ideal. Long life is vbitage,at the input (pin.2). If the voltage 1t output is, set-asdescribed. e*""Jdi that at pin 2; ttre output at pin I goeshigh (see assured if the oscillator's -. later, the meterls accuracy will be maintained until the comparator ciriuit.description earlier) and the buzzer About lV is developed acrossthe series-consoun-ds. supply drops to-about 5V per battery. inecied diodes.D3 and D4.rWhen the ESR value of the ti tfrl fnt Uetweenthe batteries was connected to the , yoltage 0V rail this split-rail arrangementwould be unneces-. capacitor being testedis about lO or less, the this lV reference. sary. It's included to enable a DC adaptor to be used acioss C4 rises above -an as alternative power source. An adaptor with an output from,I2V to 30V can be used.A regulatedtype Next Month we is best,as ripple on the supply c.puldcauseproblems. In Part2 nextmontf, will dealwith construction, ' l i t ' 'additi-on i,,' settins uD. use and inductance measurement,and in brovide a bit more information on ESR. A The Buzzer as a comparator forbuzzer operation. The detailed cbmponentslist will be included. lC3b serves March 1999 TELEVISION 321 In fhis second pqrt Alon Willcox deqls, wirh construcfion ond setting up of rhe meter, upgrcides qnd use, ond provides oddirionol bockground informotion 'bler I n pu.t I lqt month the design criteria were spccified I and a full description of the operation of the circuit f was provided. The meter i3 simple to build and the effort rcqufued well worthwhile. , is : :::.: Construction Fig. 8 shows the board layout. For convenience,'0.lin. matrix stripboard is used. The most common problem ilr9 qo.l9.".Ts- print cuts. If these are made by rwisting a d.itl lit by hanp, as I do, insteadof usingthe correct tool, it's all too easyfor the cut to be incoirplete orfor some of the print to spreadover qoan adjacent track. If a double-poleon/off switch is used,ihis is a cbnvenient point for the connection of an on/off indicator. A flashing LED with a l0kQ seriesresistor does the job we-ll:althoughit takesonly a coupleof mA, the flashing light doescatchyour eye. It is best to use screenedcable for the test leads,in order to avoid pick-up of unwantedradiation from any .7t Suitable 'ier scale, ,relproced full size. 7 5 4 3 2 I .5 E S R a l 1 O Ok H z workirg.TV line outputstagein the vicinity. Ratherthan use plugs and sockets,solder the test leadsto the ICB: we are often concemed wittr RSR values of less than 0.1O, and it doesn't take long for a plug-and-socket connectionto deteriorate and produceresistance.values greater than this. The length ofthe leadsis not at all critical. I use a 24in. length of screenedaudio lead terminatedby two 8in. lengthsof flexible wire. On- a cold, frosty morning, before the workshop has reached its normal comfortable, cosy (?) temperature, $9 leter's readings may increase,slightly. Alttrougtr this_increasemay amount to the equivaleniof less thin 0JO, the fact that accuratelow-rciistance readings are often required justifies the use of an off-the-board setzero control rather than a preset type as used in the Wizard ESR meter. This control also comes in handy if you want to squeezethe last ounce out of the batteries, but the buzzercan't be relied on when the batteries produceless than5V T9 th" outputfrom the oscillatorbeginsto fall. Also useful in this respect the ability to alte; the pointis er position easily at maximum output, to be able to observethe operationof the bulb and the correct functioning of the oscillator. This is covered in the set-up noteslater. Probeclips wereusedfor the all-importantprobes. The hooks were cut off, the internal springs were removed, then the plastic was cut back to expose more of the probes.They haveprovedto be ideal in practice,and are small enoughto often be able to get under the capacitor on the componentside of the PCB. The probesare not polarity conscious,and it doesn't matter which connection is used for the screenofthe test lead. The suggested boardsize (3 x 2in.) is slightly larger 426 April 1999TELEVISION ESRMETER - X - lrocl cut! :. ..r .::ii.i+r,.... _:{:f ' '., . Fig.8: Meiel. circuit layovt on stipboard. Board size is 3 x 2in. lo allow for upgrudes. See jex]. than it needs to be to.dccdmmodate the components. There arc two reasonsifor this: First, so that it will slot into the case that was selected, and secondly to allow spacefor future upgrades.With this in mind the set-zero control is offset to the right, allowing spacefor a modular presetshaft. The batteries are securcd with self-adhesive Velcro. It's a simple solution, and the Vrlcro will transfer several times. Apart from the bulb, the sp&ifrcation 6f ttre other componentsis not critical. The Mefer Scole The geometryof the meterlsscale(see'Fig.7) is dictar ed by the relative values of R3 and R4. If the value of R4 was'inbreased to say 10O, this would be the midscale reading and R3, being low in comparison, would hav,eless effecl Say a capacitorwith -iriil! aerESR of l0O is .bepassedon, connected.Half the signal ai.rossR3 andrtittb'6f ,its curreni will,be' diverteidt6,.reduce R3's voltage;.rvhich is the result of i6i ibtii.Ent. through the 'l*ir*,- '. . . . 1. . ! , . . .ir..; "': witli theWizard this meterdoes not diffeientidte betweena $hort4ircuit capac. itor and a really good one (with an ESR : arc-und 0.050). Now although we all kiiow ' that a short+ircuit electrolytic capacitor is quite rare, it ciio'occur and has caught me and others out. Allot of time can be wastedwhen it occurs and is missed.So I've been testing an addition that gives an audible indication when a short-circuit is present.A further refinement is an auto power-off facility. I've not included these extras at present becauseI feel it best to present as simple and economica pdect as possible initially. But spacehas beenleft for theseadditions. Gomponenl Sources I obtainedmost of the pans usedin the prototype from Maplin Electronicsand haveincludedthis company'spart numbers in the components list. The buzzer and meter movement were obtained from CPC. For correct operationof the oscillator it's vital that Cl and C2 are good-quality polystyrene capacitors. : ,l 'n lnlernal view oJ ihe meter. continued on Page 436 ffi T E L E V I S I OA p r i l 1 9 9 9 N . 4,27 ESRMETER continued from page 427 bulb' A mid-scale reading of this order may be more appropriatefor testing surface-mounted electrolytic capacitors,which seem to have higher ESR va.luei. ! have no data on this type of capacitorat the time of writing however. Anyway, the value of R4 used here,2'7{1, doesaffect the sourcevciltageto an extent that has to be considered.The current that -flows through the bulb is controlled_ the settingof VRl. R3, being only le, does by not af-fect operationof the oscillatoi. $e scale calibration with an 0-100 dial ideally follows the rule Leave the set-zerocontrol at minimum and observe the-operationof the bulb uy ttit.ting on with the qrgbei shorted together. vou *iir see the pointer deflectrrlcrrtrren"lil;;ir";;;ui"iy.;".pdownrothe stabilised"position. Once the oscillator's output has beenset, adjust vR2 for full-scale oenectionw-iirr i;;;.;;, shortedtogether. ninaity, centrethe control knob. Using the Meter nxperi-ence with the meter providesthe bestguide as to wh;t ESR value to "ip""t oi ;;;; capaciror.Some =(R3 Reading+R4v(R3 +ESR) +R4 x r00. ffiT*iJ,iff:il#t,::tiT'l#Y"""",T#"J,".TTi'; uesthat somenon-linearity the cjrcuitis apparent, electrolyticcapacitor_.of in t00pF oi-over value, you the resultbeinga-slightdlparnrrefrom this rbrmura. a readingclose to this and cerrainly itgtJ^"Id Because this,it's betterto useeitherfixed resistors below0.5h. of to calibrate scaleor copyFig. 7. If a standard the 90' There * ,orn" exceptions however. moYement a differentsiif is used, is easyenough trremtrereas they caniuur" "ooruri;;. I,ll mention of it A^irih*;lsRtoreduce.olenlargb-thqscalebyphotocopyinE. valueis to be eipected yrth ltF, ligh-vorh;;ei;- Inpracticesignar the becomes athigh var- ;#i%:!E:X'r?l3lY"'[119,1*ft,:"d:d#ti":il"# s9 rory ESR letrlnS .::', is. The first consideration the oscillator's-output level. rtutt-up"o.pon"ni. n"iog 6p"raiJin a pc context, its with thespecified lamp,the oscillatorwil wbrk down Fsi iJil;ilp"rr-r an e-xample new450v.rype a 4t to peak-to-qeak bearin mind that the oscilla- "tlt ;*;;;Uuce a reading But JV of thebrderof:30f,I At the tor's outputsetringis not importantg ilryt{ . tru--scale otniq eqoir rhe.qnge. , t9u.Eetrnp"r,oobpr, deflectionissimplyadjustedby-vR2.wit_h.thelestleads:ryqgir;;ortnrriao"*i:prpioJ.ur.adingof0.le sho{9!together'I,owsetting]ofthebircilIator:soutput<iireisiisau}f--:-:.i---:'.l1tr+-.lI provides longer battery-life,'iieduging livel it a the Table l, from Dubilier,prwides a usefulguide,in whichthe bulb ceases functional.1 qery[tor. t9 addition, ytu ar" unsure ir whatreading expect to it,s Stre testsignalcanhowever so low at highEsR values "ury "nougtiio *ut"'u "o-f*iro" be *iiri",i-iili;; thataccuracy suffers. practice oscillator - of rr9- yoor?"il-stocked In an output luy-J"r""t oiyti"r. about5V peak-to-peak a goodcom-promise. is The-meterhas good protection against placingthe rf an oscilloscope not available, followingsim- probe, u"ros u .f,.g"d .upu"it-, is the But this shouldof ple method beused. can Connect 1o resistor a beiw""n "ourr" u" uuoia"a. rfr" onryieui Juut" for concern ^uie",jiiig;: is thetestIeads turntheset-zero and controlVR2 (shown . the.'mainsmootfring block,,i.". u *an, incorrectlyas a presetiri ric, "i;t il*]l'ii-""paciior. we att tnow tr,atnis capacitor. .s* -g-.tql [ti"r*t: wise.Advancb sctting wil fas1, the of slowly.Iust:after . can abtlnb;".rrif1f pun.l *n"o " piLr-suppty has,: the half waypointtheoscillatorwill startup andthemeter's faibd l; siilt up.If you are-ofthe type with a tendency pointerwill deflect.c1rry oq.yntil th-e-buzzer iounds ro suchacciJent,iiwour,l ue fruiiiito wke a couple: steadily. thispoint the oscillator's Ar outputshouldbe ;F;; 6ack-to-babk across merer,s the inpur.,, cloqeto 5v.peak+o-peak. Note that with eachadj.ust- E F"fy rrris stiouta liotect the meter,but it won,t help your mentthe pointerwill twitch briefly as the bulb se[des, heart- ot yo'otprobes in the event of sucha misforgivingtheimpression thepotentiometer no5r, that is tune.rt'sgLoJpractice al*rr*ga irtit capacitor t" with Table1: TypicalESRvaluesat 100kH2... I Un '- a mains-type bulb - it is always reassurineto have a visual indication that little chargeremains.Seewarning note later. Capacitancevalue Voltage rating ltrF 2.21tF 4.7pF 10pF 221tF 471tF 471tF 100pF 100pF 2201tF 2201tF 4701tY 4701tF 1,000pF 1,000pF 2,2001tF 2,2001tF lmpedance* 4Q 2.8A 2.4A 1.9c) 1.3c) 1.3cr o.7a 50v 50v 50v 63V 50v 25V' 50v 16V 35V 16V 35V 16V 35V 16V 25V 25V, 35V 0.scr 0.2scr 0.25fi 0 . 11 4 Q 0.114c) 0.065fi 0.0650 0.041c) 0.036ct 0.034f) *When new - low-ESRtype. Inductonce As the meter operates l00kHz, any inductance the at in circuit under test becomes significani. The loudspeaker that reads.8C) your coqventionalohmmeterapp"*s on to be nearly open-circuitwittr ttre ESR meter. This propert_y be quite useful. When testinga line can oxtput stage for exampleyou might find that there,sa short-circuit acrossthe hansistor.In this eventthereare in generalthree possibilities,(a) the transistoris shortcircuit, (b) the line output transformerhasa primary-tosecondaryshort, or (c) the HT line has a short-circuit across it. If the short-circuit is still presentwhen the ESR meter is used,the transistoris almostcertainly the culprit: in the other two casesthe ESR meter will give an open-circuitreadingbecause the inductance the of of transformer'sprimaly winding. operateby measuring, effect, the in . Video headtesters inductance the head.Its impedance of falls as the gap deteriorates with wear. Althou;h this meter operates at a frequencythat's inappropriatefor a video heid, it can 436 A p r i l 1 9 9 9T E L E V T S T O N and considering the fact that ESR is an in-phasecompoient, I have made the assumptionin my calculations that ESR amountsto the samething as an equivalent fixed resistor. Other uses for the meter emergethe more it is used. For'example, non-electrolytic capacitois can be measured and their capacitance estimatbd.But becauseof the different types of capacitor construction in use, I can't coine up with any hard and fast rule. A lower limit for measurement about 0:lFF. There seemsto be less is Anotogue v Digitol the and less needthesedays to measure actual value of In dealingwith the problem of in-circuit ESR measure- a capacitor. With line output stage tuning capacitors mentI've usedtraditional analoguetechnology.But, as and timing components'a conventional capacitance is often the case,there's anotherway of doing things. meter is more appropriate. Bob Parker, an engineet,fdown under' who was conThe ESR meter is one of those things that, once you vinced of the importanceof such an instrument, hrst have one, you wonder how you ever managedwithout tried analoguecircuitry. After "a few fairly unsuccess- it. Hats off to whoevercame up with the idea - it's not ful attempts"he opted for a digital approach.His solu- mine. I've just taken this opportunity to sharewith you tion'is to use a 7)log processor,with, instead of a the course I adoptedto end up with the solution pre,sinewave a test signal,shortcurrent pulsesappliedto sentedhere. I haven't clappedeyeson the Wizard yet as the capacitorbeing tested.The resultantvoltagepulses, we can't afford one down here in Wales. I'd like to which are.proportionil to the electrolytic's ESR, are know how the Wizard designer approachedthe probcompared to the level existing on a fttmp generator. lem, but no information has come my way. Time measurementby the 286 processor determines The idea for my meter was triggered off by the the amplitudeof the pulses. Wizard. When I first read about it I was impressed.It .As far as the power,requirement is concerned, tliere's would test that most troublesome all components, the of a parallel in the form of a remote-control handset. The electrolytic capacitor.Not only that but.it would do so LED is pulsedwith a high currentfor a short period, the in-circuit, ignoring associated components.t liked the averagecurretrt drawl being low. The brief high cur- idea of a conventiohalmeter movementwith its easv'to-interpret rent is supplied by a reservoir of stored power in an . scale, also the buzzer feature for quick electrolytic capacitorthat's wired across the battery's checking. But the meter was shroudedin mystery and connections. its price tag was beyond me. So I decidedto have a go Friendly rivalry between the analogue and digital myself. camps has existed for a long time. This brings to mind an old story that sums it up well. Two male engineers, Development . one specialising in digital design and the other in ana- A clear picture formed in my mind as to how to go logue design, are working together in a lab. A nude about it. My idea was to supply a low-valuc resistor .: femalc appeel! at the door, attracting the attention of (l0Q) with a constant-current l(X)kHz sinewave, ,, both men. This vision of beauty announces.that every - amptify and rectify the resultant ;voltage waveform trlten'ieconds she'will reduce'the distance betrveen hei- acroSsthis resistor and feed it to h meter movement. [n r::l'selfand the engineers.byone half. The digital engineer thii situation thb meter is to be set at full-scale deflec,r:lool3Sdisappginted and cries "that's terrible, she'll tion. The test leads were to be connected across the . never get here". Xhe analogueengineer smiles and then resistor. Now ifthe capacitorbeing testedhas an ESR rcplies i'that's OK she'll get close enough". ofsay 10f,1,the voltage acrossthe resistor would fall by half. Thus half-scale deflection would correspond to an More on ESR ESR of 10Q and so on. A very low ESR (good capaci(E/ea Parker ronics puts tor) would produce a near-zero reading while a poor Australra, February 1996) ,@ob it this way. capacitor would have little effect, the pointer remaining "The electrolyte has an electrigal resistance which, at near full-scale deflection. The result is a meter scale along with the (negligible) resistahceof the connecting in opposite senseto that of the Wizard. leads and aluminium foil, forms the capacitor's equivaWithin a couple of monthsof the startof development lcnt seriesresistance.Normally the ESR has a very low work on the project I had a working prototype and value, which stays that way for many years unless the decided to write an article about it. Then, at the rubber seal is defective. Then the electrolyte's water eleventh hour, I had secondthoughts. Something was gradually dries out and the ESR creeps up with time. naggingme. The meter looked OK, did its job, and othThe electrograduallycomesto act like a capacitorwith ers were happy with it. But after using it for some time its own internal seriesresistor. . . Heat makesit worse. I felt that somethingwas not quite right. If an electro is subjectedto high temperatures, My main concernwas that it seemedto be very sensiespecially from heatgenerated internally as a result of large tive to the inductanceof the test leads.This impedance ripple currents,the electrolytewill start to decompose meant that even with the test leadsshortedthe reading and the dielectric may deteriorate- the ESR will then could not be brought down to zero. I had introduced increase more rapidly. To make things worse,as the measuresto offset this, but in this connection a more far ESR increases doesthe internal heatingproducedby seriousproblem emergedafter some further use. so the ripple current.This can lead to an upward spiral in When a capacitor with a very low (near zero) ESR the capacitor'score temperature, followed by complete was being measured, pointer would vary about the the failure - sometimes even explosive , . ." zero point if the distance between the test leads was Both Bob (Dick Smith Electronics)and Ray Porter,in altered. If they were close together, their inductance an article on ESR meter designin this magazinea few would tend to canceland the reading would decrease. I yearsback, mention the use of fixed resistorsto assist was aware how important it was to be able to differenwith meter calibration. Armed with this information. tiate betweensay 0.5O and 0. lfl or between 0'lfl and give a irelative indication of the head's 'don1thave,a collection of headsin various statesof health to be able to confirm any figures, but it seems that new headsproduce a reading of about 20 while worn headsproducea readingofabout lf). Inductorswith millihenry values, of the type used in EW modulatorcircuits, normally give an open-circuit reading.But ifa shortedturn is presentthe inductance ' dropsdramaticallyand the meter's pointer will deflect. T E L E V I S I OA p r i l 1 9 9 9 N 437 ESR METER zero.This.wasa designweakness, and I was not happy. complexity. To do away with it meantthat I neededa At this time Bob Parker's K7204 ESR meter became higher supply voltage. The use of two pp3s in seriesto available.I had one with which I could make a com- obtain this may seemto be a backwards step,but isn,t parison,and noticed the samesensitivity to inductance really. The meter now takeshalf the currentusedby the that I was experiencing.Both metersmonitor the volr first prototype, and will regulatedown to less than 5V age acrossthe capacitor,whereasthe Wizard measures per battery.In,fact the T:t9llgadinC remainsunchanged the current through the capacitor- this was clear from over the supplyrange l0-30V with the oscillatorset at its scale. 5V peak-to-peak. I went on to build a little circuit to do just that and,lo Now,-almost a year after building my first prororype and behold,this over-sensitivitydisappeared. effec_ andquite The a few versions later,I havepresented'this _;y tive lead impedance dropped dramitically, and that final (?) solution! which remainedcould be iimply compensated by for meansof the FSD preset.So it seemedthat the Wizard Worning yay yas the right way. All rhis can be explainedusing It seemsthat forgetting to dischargethe main smooth_ the relevantmaths,but I'm not about to brushup on my ing block or HT reservoir capacitor before measure_ thcory and extendthis article longer than it is aieady.' ment is a more frequent occurrence than had been that I had to scrapmy original expected.When this happensR4 at least . Reluctantly,I-accepted will blow. As ideaand starrall-overaggl on Thir was by nbw becoiling replacing components, stripboard is a messyjob, I an obsessionwith me - I had to come up with the besi strongly recommend that protectionis built in. Aimall solution,and it had to be.the simplest. board with two 1N4007diodeswired back-to-back and Certaiir things had to go. After s-ome I realised that a lA (N25) circuit protector use in serieswith one of the qlugs and socketsfor the test leads were out ofthe ques- test leads can be mounted on the back of the meter tion. Their increasingcontact resistancemade low-o-hms movement. readings unreliable. I had also been determined that the meter should operatewith a single pp3 batterv. Thonks To this end I had built a DC-DC converter io provide I have to thank Martin Pickering for his constructive a negative supply line. This provided operation .iown to commentsafter testing an earlier, voltage-sensing proto7V. But it used 7mA and geatly increased the circuit t)?e meter. Componentslist Item R 1 ,R 2 R3 R4 R5, R7, R9 R6,Rg,Rls R10 Rl1 R12, 13, 14 R R R16 VR1 VR2 Value/type 3kQ,1yo 1Q Order code M3K M1R M2R7 MlOK MlOOK M91K M5K6 M56K M2K7or M10K WR39 JM71 2.70 1oka 100kf) - 91kO 5.6kfi 56kO 2.7K1or 10kfl* 500Qcermet preset 10kCtlinearpotentiometer *Valuefor current,economy C1,C2 C3,C4,C7i c5,c6 47OpF,1% polystyrene 0.1!F miniitur'e ri;sindipped 22iF,16V TL082CN, 1N4148 Flashing LEDplus clip Miniaturewire-ended 28Y,24mAlamp 100pAmeter movement DPSTswitch Miniature alarm ABS box type BM22 Two PP3splus clips BX53 RA49 VH09 RA71 oL80 OY96and W40 BT44 CPCcode PM11125 RD17 CPCcode LS-M3 JP47 YXOl HF28 HF21 D6 [c1, lca lc2, D1,D2, D4, D3, D5 LP1 M1 SW1 Buzzer Stripboard Case Knob Batteries Probeclips cc83 Order codes are Maplin,s unless otherwise indicated. 438 A p r i l 1 9 9 9T E L E V T S T O N OHMS -.oix 7 5 4 3 compa re E S R a t l O Ok H z changed. ESR metergets An aroundthis problemby usinga test (or frequency pulserate)that'shigh enoughfor the capacitive reactance to be almostzeroohms,leaving just the ESR as the measurement. Meosuring ESR ESR obviouslycannotbe measured directly,usinga conventional ohmmeter,so a meanshasto be found 'get to'the ESR to that'shidden insidethe capacitor. numberof A ready-made meterdesigns and kits are now available measuring for the ESR of an electrolytic capacitor incircuit,usingcold checks. They achieve success simplicityin and varyingdegrees. of a suitable Use meterenablescold checksto be madewithout the risk of any furtherdamage occurring. Strictly speaking is the impedance it that's beingmeasured over a particubut, lar rangeoflest parameters, can it be shown that this presents more or Iessthe samevalue. It is all too easyto over-complicatethings when it comesto ESR. Thereare thosewho arguethat ESR meters don't measure ESR the precisely. But, in the real world, how precisedoesthe readingneed to be? It really doesn'tmatter.The service engineerjust needs to know,as quickly as possible, which capacitor causing trouble. is the An ESR meterdoesjust that!Once technicians have becomeaccustomedto using an ESR meter,they wonderhow they ever managed withoutone.Althoughthe ESR variessomewhatwith frequency, we can in practice regardit as beinga constant in-phase component,and calibrate meterusing our fixed resistors. This is useful,as the meterwill alsoservewell as a lowohm meter. So.if an ESR meter doesn't what readings measure capacitance, can we expectfrom good and bad capacitors usingsucha meter? a How do you know whether capacitor OK or not?The curve is shownin Fig. 2 givesa practical ideaof the sort of ESR readings rvith good thatshouldbe obtained capacitors differentvalues. of rule Thereis no hard-and-fast horvAll science. ever- it's not an exact usedto. it needs a bit of getting is This doesn't takelong:just measure the ESR of a f'ewnervcapacltors.Try l, 10,47, t00, 470 and 1,000pF. will find thatvalues You quite of 47pFandabovemeasure with thebuzzer low.0'5O or less. turn-on coming (thebuzzer on The pointcanbe varied, later). see The equivolent series resistqnce (ESRI of qn electrolytic copocifor is o relicrbleindicqtion of its condifion. Alon Willcox's firsr ESR mefer".detign, published in these pqges some five yeors a9o, wqs very populor. This Mork 2 version incorporoles severql improvements, in porficulor q simpler oscillotor design ond single-botfery operotion simplified equivalentcircuit tancebut, when it deteriorates, it of an electrolytic capacitoq increases impedance the present. seeFig. l, is usuallyshown The lower the ESR, the betterthe when providing a briefexplanation capacitor! of what ESR is all about.In addiElectrolytic capacitorsusedin tion to the ideal capacitor Xc, a switch-mode(chopper)power supsecondcomponent present.It has plies and thosemountedclose to is a significanteffect on the capaciheatsinkstend to run hot. Heat is tor's performance,and is referred inclined to dry out the electrolyte to as the equivalentseriesresistand, in time, a capacitormay develance(ESR).Electrolytic capacitors op a high ESR.This will itself are usedmainly for decouplingand, introducea power loss - and more to a lesserextent,for signal couheat!The effectoffailure ofthis pling. This being so it's important type in a power supply can be catathat, for optimum performance, the strophic.For example,if the capac(AC resistance) the impedance of itor is in the HT monitoring section capacitor as low as possible. is of a TV set'spowersupplythe HT An electrolyticcapacitor'sESR voltagemight rise, damagingthe is mainly determined the condiby line output transistorand maybethe tion of the electrolyte(paste)that field outputIC. separates foils. The electrolyte its This type of problemis more increases component's the capacisignificant when a set is startedup from cold, as the conditionof a faulty electrolytic capacitoris worsewhencold.Thus cold checks are by far the bestapproachto testing! Problems with electrolytic capacitors, particularly thoseused in switch-mode powersupplies, are caused so much by a change not of capacitance valueas by an increase Fig. 1: Simplified equivalent circuit in thecomponent's ESR.Thus of an electrolytic capacitor. Xc removalof a suspect capacitor to represents an ideal capacitor. lts checkit with a conventional capacreactance moves towards zero itancemeteris largelya wasteof ohms as the frequency increases. time-Furthermore faulty capaciXc = l/(Zt fcl. The value of the a equivalent series resistance ESRis tor may be overlooked because its determined mainly by the condition capacitance valuehashardly of the electrolyte. 76 2 D e c e m b e r 0 0 4T E L E V I S I O N impo.rtant point is just how low capacito-is with valuesof 47uF and abovemeasureAt 47018 and ovr., i the readingis closeto zero'ohms. If, in practice,a 1,0004Fcapacitor produces readingas high as O.SSI, a rt's no good! i: ES8(o) Anqtd$i,i'ditiin"l , dtsPlg)B.ri,. -.. , Digital..methods measurement bf andlisiildy are'generallyregarded as pro,vldrng results. &ore accurate F9r mpny applications rhis is true. but itjs nqr:,45pessarily wi*r gSn so measureineriflThere two wavs ire of interfacingthe,capacitor beinl tested' eiffi the m6tir:ftre capaciicir can be connected parallel-with in the test sign4l.g"ourqe, shownin as \_ fi tting.twollehds.tor6actlprobe:;It provides.cancellation"toi,laige- . extent,;but:thissolution.is U'it .. , a rmsyin.r'seand'toconshuct.The ""cries method ofiinterfacing does ,;., not sufferrfrom,this.ilrawback;so the useof;conventional test leads , becomes' acceptablel don't know ll y h y t h i s e f f e c t o c c u r s - I j u s:t,. found out the hard way. . . Although we have6ecomeused to_digitalreadoutsnowadays,for ESR measurement there is-little doubt that a moving-coil meter is the.best type of display.It gives a raplo, ei$y-to-rnterpret indication of the conditionof the capacitor. After someexperience using it, of oxe getsto know wherethe pointer shouldapproximately with good be capacitors different values. of Indeeda meterscalebecomes almostunnecessary.know of I peoplewho haveusedthis type of meterquite satisfactorilywithout ever having takenthe trbuble to fit a scalededicated ESR measureto ment. Layouio( Non willcox's Ma* 2 ESR To repeat:it's not an exact scimeF,ron stripboard. n" n4z incorporates severol.improyements, includinga simpler""riil.i";-i;;b" encebut, with someexperience, i,ii;igb_bottery operalion. sensitifi.df0lttiri[dluctiriie,ofithe,,l ffis".ii,ii'be.overcome ty $! le3+,r - If a digital ESR readouti; ii;ad. the capacitormust shuntthe test signal.,Withan deal,capabito4 the resultrwill be:z0ro,ohms; d.z&te.,.: an :t display:.-with badcapacitorthere a. will be d hieh rcading;with linle s_h_untlng of. the test-signal. away We are interbstedin ESR viues of 3Q or less,rbut digital meter a gives readingsfar higher than this. It's not a major problem,but can grve nse'to superfluousinformation aSfar aSESRtmeasUrements r_ are j concemed;A inore.important factor is ftat the:bqraltdmetnoa results in a signifiidrftlniiease in,tne read::^ : ings obaiiied&ecauiff 'of,ejri:i:Ssive i Fis.3(a);Wiii"i;?:ii6b', irbi.' t#'rie. ItF* ,Qgq$anr; qf9:3lgt.' gl9se Rsample.Value cfiosen for optimum meterscale ptb ?d anp Fig' 4: The basic ESR meter circuiL new version. lcl and IC2 require positive and-negative supplies at pins g and 4 respeaiiely. Further circuitry is required, see nert month, to generate tne sim-riit iujpfu and provide a buzzer comparator. one soon gets to knoy whfglrwill lly capacitance providenegli_ , capacitoris causing_ qo.ublethe by .- gible oppositionficjto it. knowingroughly wherethe ESR'': :t 'meter's pointer should be with a Waveform: Analysis of a square_ good one. one argumentthat's wave has beenused,and l'vL triea sometimesput forward against the ,this myself. The results are a bit use of a moving-coil movementis unpredictable however.I had a lot that the movement will be damofiroubre trying to preservethe aged should the meter fall off the waveform intaci at the mv level to bench.I have a solution to this give a useful, predictableindicaproblem. If you are inclined to be tion. It's not *:orth the effort. A string glumsy,attacha piece_of sinewaveis so easyto generate and betweenthe mererand the bench, gnplify that I cannotsJeany.lusti Iong enoughso that the meter ncition for incorporatingsquare_ comesto-a halt just before it hits wave analysisinto the dEsienof an the deck but not so short that you ESR metei. '' dorittgetabitofajolttoservLas'117'l'*"1*. ( .. ' :a'ieminder. , An improved ESR.meter Thr meter presentedhere is similar TesFsignol porumeteru to the one describedin the Amplitude: To test for ESR or for March/April 1999 issuesof actual capacitancethere are no con-. Television. Since then the use of an straintson how low the test sisnal ESR meter to check quickly for can be as far as the capaciior ii faulty capacitorshas Lecomewell concerned. Taking into account established. The original circuit power consumption,and the probworks well and has stood the test lems associated with lowJevel sigof time, but feedback from the nals of the order of microvolts, hade has prompted me to make noiseconsiderations etc.,a level of someimprovements.Theseinclude about 5mV peak+o-peak seemsto single-battery operation and be a good compromise. improved temperature stability. The new circuit remainsstable Frequency: The time period down to 6.2Y, and consumes about shouldbe short enoughto zero out l3mA. Becauseof the improved the capacitivereactance. 100kHzis temperaturestability of thl new a popularchoice.At aboutthis freoscillator circuit, there is no need quencythe ESR and impedance for an externally-available set-zero convergewith the type of capacicontrol. tors in which we are interested. Apart from that consideration, The oscilloior cirrcuit lOOkHzis about the top frequency An IIF oscillator or pulse generator at which a predictablegain of up to with a stableoutput over a reasonten times can be obtainedwith able supply voltage range is the readily-available, low-cost operaheartof every ESR meter.ICla in tional-amplifierICs. the new circuit, seeFig. 4, is the Rememberthat if the rate-ofsinewaveoscillator in this design. change the voltageis fast enough, The simplestway of generatingof a sinewave.is incorporate the to in oscillator's positive-feedback path a network originatedby Max Wien in 1891.It ensures that the feedback is an in-phasecomponent at only one frequency,which is fixed by the rRCvaluesused.At very high frequencies presents lowC2 i impedancepath, while at lower frequenciesCl becomes effective an open-circuit.At somepoint in betweenthere will be maximum output from the network Cl, Rl, C2,R2, which is refened to as a Wien bridge. The RC values used here'resultin oscillationat about lfi)kHz. There are two simple methods of stabilising the output level with an op-amp Wien-bridge oscillator. The method traditionally usedis to include a bulb in the nelativefeedbackpath (between-pinsI and 2here). This was the approach used in my 1999design.There has been some misunderstandine about the bulb, because ttre Oifof ferent specificationsused in US literature. I went into the maner in some detail in the 1999 articles. The correctspecification is 28Y,24mA. The principle behind the use of a tungsten bulb is that its resistance increases with the current that flows throughit. If a bulb's resistance measured, small is the current from the ohmmeterwill increase resistance, its When employed correctly in this application the bulb doesnot come anvwherenearincandescence.decidI ed to use the lamp then because of its elegantsimplicity and extremeIy low distortionfigure (0.0025Vo). With the new design I wanted to reducethe operating voltageof the 7B l.)ecemhcr ,)OO4 TFI F\/lqlr.)\l , L w h o l e m c t e r s o t h a ta s i n g l eP P 3 battery could be usedas the porvcr s o u r c ew h i l e s t i l l a c h i e v i n gv e r y The lorv po"vcr consumption. problem '"viththe use of a bulb is t h a t i n t h e s ec o n d i t i o n s h e b u l b ' s t temperatureis not sufficiently far away from the ambient temperature to ensufegood stability. so this time I decidedto use the brute-forcemethodof diode stabili s a t i o n( D l , D 2 ) . The idea here is that when the output from the oscillator rises above the conductionpoint of the diodes the negativefeedback the increases, output settling at an amplitude which dependson the of characteristics the diodes. In this case the net result is a sinewavesourcesignal acrossR5 with an amplitudeof about 6mV peak-to-p"uk.Diod. stabilisation introducesgreaterdistortion, but this is not important here. To maintain oscillation,the value of R3 must be over trvice that of R4. A preset resistor, adjusted to just sustainoscillation(lorvestdistortion), is usually used in the R3 position. I decidedto use a fixed value that's a ferv ohms on the high side, to ensurereliable oscils l a t i o n r e g a r d l e so f d i s t o r t i o n . Interfocewith rhe copocitor being tesfed The interfacewith the capacitor being tested is the crucial part of the meter. It took me a long time to get this right. SeeFig. -5. The waveform acrossR5 (the source resistor) is not an ideal,constant-voltage source,because the needto of '--,.nclude the sampleresistor(R6), rvhosevalue must be comparableto the ESR valuesin rvhich we are interested. The ESR of the capacitor being testedforms part of a potentialdivider rvith R6. Thus if, for exanrple. good 1,0007rF a c a p a c i t o r v i t ha n E S R o f a b o u t 0 ' l O i s c o n n e c t e do r t e s t ,R 6 i s i c { ' f b c t i v c l i n p a r a l l c r v i t hR - 5T h i s y l . I n c a n s h a t t h e s u p p l y - s i g n a lo u r c e t s . i \ l c s \ h r ' t ' a u s rr' v l r c rtrr c i l p : r c i l o iIs b e i n gt c s t c c lt.l l c c o n s t i r n t - c u r r e n t s o u r c ct o l l 5 i s s h l r r c trl v i t l rt h c t : S I l u r r d[ { 6 i n p l r a l l c l . '['hc v o l t a q cr i , u r ' c l i r r n l c v c l ir o p c t la c r o s s 1 6 t s : rr c s u l to l l h e 1 l , l r i l , ' i l 1l l t t , ' t t . - l lrl r e , l r P i r r ' i t r r t ' l r c i r r g{ c s t c t l i s l r n r l l l i t i c cu n t l t h c n l r l c t c c t c cb y t l r c r c . l o l t l r c c i r c u i t . i l l t h c t r S I { o l t l r e c r r p a c i t o rb c i r r g t e s t e ( li s c q u a l t o t h c v a l u c t r l l { 6 . l u r l l o l t h c s t r p p l yw a v c l i r r r n r v i l l -l'lrc bc passctlorr. supply rvavc. t I r l r r n i s r r o t i r r t l c p c n r l c r ro l l l r e I o a c ll t o r v c v c r - . l t h c I : S I t i s l c s s I than the value of R6, as rn rnost casesit is, the lvavefonn voltage acrossR6 increases. A s t h e E S R r i s e sa b o v e t h e value of R6, the latter becomes less effective. The result of all this is a non-linear scale, expandedat the lolver range and somewhat l o g g e do u t . T h i s i s i d e a l f o r t h e I p r e s e n ta p p l i c a t i o n ,b e c a u s e n s o m e c a s e si t i s i m p o r t a n tt o b c a b l e t o d i s t i n g u i s hb e n v e e na v c r y l o w v a l u e ,c l o s e t o z e r o , a n d o n c of about 0 -5Q. Internol view I have achievedlow current conof the new s u m p t i o na n d c i r c u i t s i m p l i c i t yb y ESR meter. tusing the feedbackcurrent and fhe test leod on comprornisingsomervhat the connections are ol source. ideal. constant-voltage the bonom, with proteclion diodes bet,tveen them. Nexf month i t I n t h e c o n c l u d i n g n s t a l m e nn e x t I r r r o r r t h' l l c o m p l e t ct h e c i r c u i t description,deal rvith sonrepractical points and protectionntethocls, nts provide a detailedcontporre list I and a stripboardlayor-rt. 6 m V p - pu n d e r 0 6V P-P anncr2nr oPen-circuit ( l C l a p i n2 ) : : ; : : : ' , " condirions i i Y""""' I i t lR4 1oo() / I i I Esn Constant-voltage source (from osc f e e d b a c kl o o p ) Fig.5: The method of test capacitor interface used in this nreter. The source voltage is not a true constant voltage because of the need for R6, whose value nrust be cotrtparable to the ESR of the capacitors in which we are interested. Current economy and circuit simplicity are achieved by using feedback current front the 'logged' oscillator circuit as the source fed to the capacitor under test. The outltttt is inversely out in relation to ESR. l l l l \ ' l \ l r r ' , meter,with o suggestedstripboqrd loyout ond Wittcox'slotest ESR component specificotions so 1999issues, only a briefdescription is given here. The frequencyof the Wienbridge oscillator is approximately equalto ll(zfiRq when resistors Cl Rl andR2 and capacitors and C2have equal values.At this freshift quencythereis no Phase acrossthe bridge and thus maxiCircuir description At mum positive feedback. resoFig. 4 (seepage78 last month) nance,the upPersectionof the netshowsthe basic ESR metercircuit. work (Rl, Cl) hastwice the imPedThe important featuresof the oscilanceof the lower section(R2, C2), lator and test interfacesections loss so there'sa transmission of There is were coveredlast month. the oscillation, over1/3.To sustain no needfor a regulatedPowersuPall gain (ALC) must be greaterthan ply. Just to remind you, the amPliloss unitv.The transmission tude of the HF output waveform throughthe network is offset by the from the oscillator(ICla) obtained bY gain determined the ratio I + which is setby the characteristics, (R3/R4).In this circuit theALC of are virtually temperature-stable, would be more than the threetimes the two diodesDl and D2 in the were it not for diodesDl required between negative-feedback Path and . andD2, which overridethe effect pins I and 2. The amplification above. of R3 as mentioned bY levelsprovided the detection of The following two stflges are otherstages setbY the ratio of (IC2a and IClb) are amplification resistor lnd feedback lhe source rvith no needfor opera- straightforward, This is standard valuesused. C3 circuitry.Capacitor in conection practice. way The tional-amplificr (IC2b) stage the feedto the detector amPlifiers in whichopcrational anYDC comto is included remove red cove in somedetailin work rvas and alsoto rctluccsensitivity oonent in my articles theMarch/APril I n Part I last month I dealt with and I gSn and its measurement, feathe I described significant turesof my latestESR meter design.I'll startthis month with a descriptionof the basic circuitry used. (mainshum or to low frequencies Rl2 setsthe gain in the whatever). ofthe high Because stage. detector intrinsic gain of an operational amplifier,the forward voltagedroP acrossdetectordiodesD3 and D4 is overcomeand detectionat evenmV level is not a problem. This second, concl SpliFroil genetator ond buzzer That is all thereis to the basicciramplihers cuit. But the operational suprequirepositiveand negative is plies.This requirement provided by IC3b,seeFig. 6, which is configThereis ured as a voltage-follower. (pins feedback 100 per centnegative 7-6), so the outputvoltagemust settle at half the supplyvoltage,setby the equalratioof Rl4 andRl5. I to was pleased find thatthe circuit as with outputs lorv stable remains as +3'lV. This lower supplyvoltage rangeis quiteconsistent. as IC3a is configured a voltage Whenthe ESRrcading comparator. is lessthan0'5Q, theoutputfrom goeshigherthanthe thedetector D8. drop across forrvardvoltage The outputat pin I of IC3 thcrcfore 158 2 J r r u a r y 0 0 5T i l E V I S I O N FromRl2lC4 lcl,lcz pinI lcl,lc2 pln4 :oes high, activatingthe buzzer. .-fhe ESR level at which the buzzer is operates set by the overall gain. This point can'easilybe changedby alteringthe value of Rl2. If its the value is increased, overall gain rises and the buzzer will operateat a higher ESR level. The value of l00Q for Rl8 is chosento limit the currentfrom an external 12V sourceto a rechargeable battery to the trickle level. The overall consumptionis so low that, if you are one of thosewho remember to switch off battery-powered equipmentwhen it's not in use,an ordinary battery is OK and will last for quite a long time. Although the basic metercircuit is happy with a supply between630Y the buzzerand LED won't be. The value of 2'7kf,Jfor R19, which is in serieswith the power-onindirtor LED, gives good brightness . \ver a supply rangeof 6-9V with only a feg mA drawn. Prqcficol points As the meter operatesat 100kHz, in any inductance a circuit being checkedwill produce a highimpedancereading. If an EW coil producesa reading,it has shorted turns. Another use of the meter is where the line output transistor to appears be short-circuit.A quick check with the meter will isolateit - if the short is elsewhere, most in casesthe impedanceof the line output transformerwill be in the way and will result in a high reading.If there'sa low reading,the transistor is most often the culprit. ESR meter usershavecome up The nonwith new applications. polarised,high-voltagecapacitors usedin the line output stage(tuning f I Prlntcuts(24) +ve supply +ve' Meter 'Connecl to track slde of board Top - Fig. 6: The split-rail generator and buzzer comparator circuits. Centre- Fig.7: Suggested layout on stripboard, Left - Layout of the prototype meter on stripboard Bottom - Fig.8: The ESB meter scale, shown full size l58mml. etc.) can be tested.I've not taken the trouble to designa new meter scalefor this application,as I have of no practicalexperience such checks.It seemsto me that if such a capacitorgives any readingat all other than short-circuitit will be OK. This type of capacitordoesnot value. change I would like to think that the presentarticlejust about sums to everythingup with resPect the t 5 t ! 2 o ESRat 100kHz Cr TELEVISION 2005 January 159 Partslist Item Rl,2 R3 R4 R5 R6 R7,9,11,16,17 R 8 ,1 0 R12 R13 R 1 4 ,1 5 R18 R19 ...\ \ Valueftype 3ka 220A 100a 1A 2.7A 10kc2 100ka *68kQ 3.9kA 56kO *100Q *2.7kf2 CPC order code R E M F R 4o l l o w e d b y t h e v a l u e f A l l 0 . 5 W1 %m e t a l f i l m , VR1 c't,2 c3,4 c 5 ,6 , 7 1OkQ cermet preset 470pF low-loss high-stability*r 0.1pF cer-amic multilayer 221tF, 16V RE01881 cA02068 cAo2098 cAo1613 sc1N4't48 sc1N4004 sc1N4002 scTL802. sc00023 PM11119 D 1 , 2 , 34 , 9 , 9 , D5,6 D7 lc1,2,3 LED M1 S1 1N4148 1N4004 1N4002 TLO82CN 3mm Superbright 1 0 0 p Am o v i n g - c o i l M i n i a t u r et o g g l e s w i t c h sw-z201lz 1S00654 EN55030. 1N00772. PC00046 PC00066 8T02187 PWo0037. Seetext Seetext Buzzer 5V DC Case ABS box Testleads 2mm plugto probes Veroboard Spotfacecutterfor Veroboard PP3battery clip lead protection High-current choke See text quick in-circuitlocationof faulty achieve slimmerappearance, a I electrolyticcapacitors. anyone If boughtanother case, typeEN55029 contemplates designof a PCB the (too slim), and combined the for the project, it is importantthat halves. This might soundextravaseparate operational-amplifi chips gant,but you still end up with two er are usedfor the oscillator and the cases and theycostonly aboutf2. first amplifier stage- to avoid interference Protection mefhods between oscillator the andthe sensitive first amplifier In a letterin theAugustissuethis stage. Fig. 7 showsa stripboard yearJim Littler suggested wiring layoutfor the meter'scircuitry.Fig. an inductoracross testleadterthe 8 showsthe meterscale. minalsto protectthe metershould Don't be tempted useplugs to it be connected a charged to capaciand sockets the testleads you for tor.I can seeno problemwith this, wouldin time get problems the in andfollowedup with a letterin the low-ohmsrange.Soldered connec- Scptember issue. a valuesomeIf tionsshould usedthroughout. bc I rvhatlower thanthe l5(i7rHrccomuse2mm testleads with theplugs rnended thereis used, producing a cut off. Make surcthatyou file the reading say30Q, this rcading of probes give sharp to points. rvill be present The eachtirre the nteter coating that'son then.r a signifi- i s s r v i t c h eo n a n dy o u r v i l lk n o w has d cantresistance. thlt it is workingcorrectly. will It The case spccificd theparts in not al'fect useof thc ntcter. the We list is a bit on thedccpside. To l r r e n l y i n t e r e s t e n v u l u c sh a t o id t aremuch lower. If this methodof protection is usedwith a digital meter,the display will settleat a fixed reading. This will showthat all is well with the meterand will alsoeliminate superfluous readings. the caseof In a moving-coildisplay, will douit ble-upas a power-on indicator. The useof a circuitprotectorin series with the testleadshasbeen suggested. problemis that it The would tendto blow too easilyand requirefrequent replacement. To reitcrate, diodeprotection (D5, D6) should always incluclcd. be Any contments about high-cLrrrentchokeprotection, whichseenrs to be a r"rniqr.re andon ESR idea, measurcntcr)tgeneral in wouldbe welconrc. Youcanreach by emailat me alancsr(lr hotrnai l.com I t h i n kt h a tc o v e r s v e r y t h i n q . e t r60 2 J , u r u a r y0 0 5T E L E V I S I O N ESRvalues at,1Q0(Hz.r. Table 1: T.yRical ... t ,", Capacilaicbvatie Voltagerating tmpedih'ce* : 50v lttF 4rl 50v 2-21tF 2.8cr ' 50v 4.71tF ' . 2.4A 63V 10ttF 1.gfi , '50v 221tF 471tF 471tF 100pF 100pF 2201tF 22O1tF 47OpY . a7O1tF 1,000pF 1,000pF 2,2001tF 2,2O0pF : . 25V' 50v 16V 35V. 16V 35V 16V 35V 16V 25V 25V', 35V 1.3cl 1.3fi 0.7ct 0.5c) 0.2scr 0.25cl 0.1 14cl 0.1 14ct 0.065cl 0.06sfi 0.041rt 0.036rl 0.034cl *When new - low-ESRtYPe. ponel Anologue meters FAnuetc I t-.# zz 98278 onoers s t * i l r e r i c . I a a tultr ?*,rrlrrrrlrrrrlrtlr, o t r'rr'4 a a a Attrocfive md moderndextign Clxfce of printed scdes 4 popdqr sizes "Eosy-frf'scdes Chss eO ^1t,ttl'l'l'lrrr7, , Crder Code METERS 3V15X1MA :V15X100UA CV-15X 0-1mA CV-15X 0-100F4 Size Range Rec. Price €: 1+ 5+ 10+ 25+ 50+ :Vl5XGZ100UA CV-15X 100-0-100!A 3Vi5XSZ20MA 3V'OXIMA 3Vi6X100UA CV-15X 1004-1004 CV-16X 0-1mA CV-16X 0-100ttA at rangeof qualitydc moMngcoil metersavailble A modernand attractive prices. verycompetitlve sizeswhichcan be eithersurface or flush mounted Thereare4 popular The metersutilise well a cutout. behind panel through rectangular the a proven and robust, 90 degree deflection,pivot and jewel moving coil movemenl. 3V16XCZ100UA CV-16X 1004-100A4 M6XSZ20MA ;V18X1MA 3V18X100UA CV-16X 4-2OmA CV-18X 0-1mA CV-18X 0-100rA ;Vl8XCZ100UA CV-18X 100-0-100FA of Meters are supplied in sensitivities 100 microamps,100-0-100 3V18XSZ20MA CV-18X 4-20mA (supressed (centre zero),1 milliamps as 4-20 milliamps or microamps CV-20X 0-1mA 3V20X1MA process indication. zero)for signal graduated numbered 0-10, and are seperately Pre-printed scales available and100-0-100. 0-30, 0-100 CV20X100UA CV-20X 0-100!A 3V20XCZ100UA CV-20X 1004-100pA 3V20XSZ20MA CV-20X 4-20mA METER SCALES S/CVISXB CV-15X Blank s/cv15x10 s/cv15x30 s/cvr5x100 s/cv15xczt00 9/CV16XB cv-15x 0-10 cv-15x 0-30 cv- 5X 0-100 cv 5X 100-0-100 CV 6X {_fi+ Fixing studs on all meters (DimensionG)are M3 x 12mm Dimensionsin mm M o dA eB l c 48 58 67 D 43 E 24 F 40 H I 35 48 48 64 J W S c a | e Length CV-15X 57 CV-16X 68 cv-18x 80 1 . 5 1 4 . 52 8 . 5 5 0 x 2 3 . 5 1.5 14.528.5 61.5x28 5 14.5 28.5 72 x35 1.5 14.5 28.5 92x45 40 50 63 78.5 s/cv16x10 s/cv16x30 s/cv16x100 s/cvl6xczl00 s/cv18xB s/cvl8x10 s/cv18x30 s/cv18x100 S/CV20XB cv cv cv 6X Blank CV 6X 0-30 6X 6X 0-100 100-0-100 Blank 0-10 0-30 100-0-100 cv- 8X CV 8X cv- 8X 8X cv- 8X 0-100 CV-20X Blank s/cvl8xcz100 cv s/cv20x10 cv-20x 0{0 45 31.5 48 50 38.5 64 50 51.5 80 CV-20X 100 83 cv-20x 0-30 s/cv20x30 cv-20x 0-100 s/cv20x100 s/cv20xcz100 cv-20x 100-0-100 ANALOGUE\CVl Revision4 03/06/04 rO FaOl ANO*S SUEJECT A mOQ OF 25 PC$ AVA1ASIE FRort NATKta,lA!OlglRlBUtORs OR DIRECT plc LondonNWl OEU UK Place, Onders electronics Bayham Tel:+44 (0)2073808167 Fax:+44 (0)2078741908 wwwmeters.anders.co.uk MetersI Electrical Farnell SD80/0-100UA I I MULTICOMP I Panel PageI of I 2OO7 /08/08 , P S D S O I O - I O O U - M U L T T C O M- M E T E R8 1 X 8 1 M M O - I O O U A A P Manufacturer: MULTICOM ,Availability Availability: 1 Price For: 1 Minimum Order Quantity: 1 Order Multiple : 1 U*it ?rice: 99"5$ 4S 60 Order Code: 4433932 Manufacturer Part No: SD80/0lOOUA Rol15 : Description a a a Image is for illustrative purposes only. Pleaserefer to product description O M E T E R8 1 X B 1 M M - l O O U A , D e p t h , e x t e r n a :3 6 . 5 m m l .._. -^:": D i a m e t e r ,p a n e l c u t Orire out:63.5mm L e n g t h/ H e i g h t , : external:81mm i L - 4 Meter Movement FSD:100pA .t-n a Pitch:34mm .LO-24 a Resista nce, coil: 1 500R a Width, external:81mm :25-49 _ _Qtv List Price €9.5B f 9.38 89.t9 €8.96 E7.37 Technical Specifications r*l Product Rang;e Catalogue Page: 58s / UK2 Product Attributes Weight (kg): 0.12 Approximate weight in primary packaging Tariff No.: 90303399 Country of Origin: TW Taiwan Country in which last significant manufacturing processwas carried out ffirech::ical Oata$heet {i.95 kBi fi0ierL*qc p : i , / a c y $ l : a t c m en t I S i t er f l e p j T er r r s c f P r r c h a s e I T e r m S l f A c c er : Cc;:iTrlght ii-; 2307 l:rer*:er Ferneil UK Llmite d ALL R:Gli15 i C o p y ! - r g h t n t i l r w h o i e a r r d e v e r y p a r t o f l | i i s ! 1 i r t i s i l e* e l r n ; s i c P r er : i e r ? a n e t l i ) 4 . L a r n i f . : l i i c e n $ e d t r a n s f e r i - e dc o p i e i o . r e p : ' o d u l e ciin w h o l e o T i n 3 a ! - li n a l y m a n n e r o r : ' : t t : l ' : ; i r ' ; , , a c c c r c a n c e y , , l t ht h e t e r m s o f i r e O ' ^ n e r ' s a g r e e r : e f l | , w i t n o , , r tl n * p r t i ) t w r t ' p r e n ' r ; e rf * r n e l l U K L i m i t e d . R e g i s t * : ' * d i n f n c i a r d a n d W a i e s f i . : C { . } 8 ( F a i n e l l i s a d : v i s i o no f Lecd:, i..gl: 2QQ. Prcd ucer Rcg lstration l'lu *r be r : \'! f.f.I AKt), 4117. 08108/2007 http://uk.farnell.com/jsplElectricaliPanel+MeteTsAvIULTICOMP/SD80/0-100UA/disp...