1.Objectives: 1) To show how the platinum resistance thermometer works and how to connect it correctly. 2) To show the linearity of the platinum resistance thermometer (PRT). 3) To prove that the platinum resistance thermometer is good for use as reference temperature sensor for all the other experiments. 2. Introduction and Theory: Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a pure material, platinum, nickel or copper. The resistance thermometer in this equipment uses a thin platinum wire so it is called Platinum Resistance Thermometers (PRTs). A sealed metal tube with insulation contains the thermometer for protection against the conductive or corrosive properties of any liquids that you put the thermometer into. Resistance to Temperature Conversion The RTD is a more linear device than the thermocouple, but it still requires curve-fitting. The Callendar-Van Dusen equation has been used for years to approximate the RTD curve: Where: RT = Resistance at Temperature T Ro = Resistance at T = 0ºC α = Temperature coefficient at T = 0ºC ((typically +0.00392Ω/Ω/ºC)) δ = 1.49 (typical value for .00392 platinum) β = 0 T>0 0. 11 (typical) T < 0 1 Figure 1: The Platinum Resistance Thermometer used in the present experiment Figure 2: Wires on the Resistance Thermometer (RTD) Ohm’s Law In 1827, a physicist George Ohm published his discovery that all electrical circuits obey a simple relationship: “The current passing through a conductor is directly proportional to the voltage drop and inversely proportional to the resistance of the conductor”. I= V/R Where: I= current V=voltage R=Resistance 2 3. Apparatus: TEMPERATURE MEASUREMENT AND CALIBRATION (TD400), as shown. Fig (3): TD400 It consist of electrical board which contain Wheatstone bridge, constant voltage connection, constant current connection, two digital screens and some resistors to substitute long in wires. Have eight different popular temperature measuring devices, and a thermo well to show temperature lag. Uses a platinum resistance thermometer as a reference to accurately calibrate the other devices. Shows how electrical resistance devices and thermocouples work, their characteristics and how to connect them correctly to reduce measurement errors. Includes liquid-in-glass thermometers with safe non-toxic liquid - no mercury. Built-in water heater tank with protective guard and drain tap for safe experiments. Works with TecQuipment’s Versatile Data Acquisition System for simple and reliable recording and processing of results Built-in pressure sensor (barometer) with display of local water boiling temperature. 3 4. Procedure 1. Create a blank results table as shown in table 1 Table 1: Blank results table Table (1): PRT Calibration Standard Measured Calculated Resistance Voltage Resistance from (mV) (Ω) Specification (Ω) Reference Temperature (oC) Deviation (Ω) Error % 2. Connect reference sensor to its socket and connect the PRT to the millivoltmeter and the constant current source. Note that the PRT is connected as four wire device (see figure 1 and 2). 3. Set up the heater and ice box as follows: a) Disconnect the electrical supply b) Shut down the drain valve at the back of the heater tank c) Unscrew the lid of the heater tank and fill it with approximately 1.5 liters of clean water so that it is half full. d) Refit the lid of heater tank e) Add ice to the ice box and put its lid on. f) Make sure the heater switch is off and reconnect the electrical supply. g) Fit and adjust the black O rings to each device you are to use. Adjust the O rings so that each device is immersed in the heater tank water by between 70 mm and 80 mm. If necessary add more water to the heater tank. 4. Put the reference sensor and the PRT into the icebox (through the holes in its lid). Wait a few minutes for the reading to stabilize and record them (the reference temperature should be between 0 oC and 1 oC). 5. Now put the device into the heater tank (through the holes in its lid). Switch on the heater and note the reference temperature. 6. At interval of 10 oC (shown by the reference temperature), record the input 1 readings of the millivoltmeter. 7. Stop the experiment and switch off the heater when the reference temperature reaches 100 oC. 4 5. Results and Discussion: Given that the constant current is 1 A use Ohm’s Law to calculate the resistance of PRT for each raw in your table. You should see that the calculated resistance is directly proportional to the measured voltage. Plot chart of resistance (vertical axis) against temperature (horizontal axis). Start the vertical Axis at 100 Ohm. Add to your results table and chart the standard resistances given by table 2 that matches the reference temperatures. In your chart draw a straight line through the standard values. Note any difference between the standard and your measured resistances. On your results table, find the difference between the standard and your results (the deviation) and calculate the percentage error Percentage error = (deviation / standard) x 100 Table (1): PRT Calibration Standard Measured Calculated Resistance Voltage Resistance from (mV) (Ω) Specification (Ω) 100.9 100.9 100.35 108.8 108.8 107.79 110.6 110.6 109.73 112.3 112.3 111.67 114.5 114.5 113.61 116.3 116.3 115.54 117.9 117.9 117.47 119.8 119.8 119.4 121.6 121.6 121.32 124.2 124.2 123.24 125.9 125.9 125.16 127.9 127.9 127.07 130 130 128.99 131.8 131.8 130.9 133.5 133.5 132.8 135.6 135.6 134.71 137.4 137.4 136.61 139.6 139.6 138.51 Reference Temperature (oC) 0.9 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Deviation (Ω) 0.55 1.01 0.87 0.63 0.89 0.76 0.43 0.4 0.28 0.96 0.74 0.83 1.01 0.9 0.7 0.89 0.79 1.09 Error % 0.548082 0.937007 0.792855 0.564162 0.783382 0.657781 0.366051 0.335008 0.230795 0.778968 0.591243 0.653183 0.783006 0.687548 0.527108 0.660678 0.578289 0.786947 5 6. Conclusion: The present results have shown the expected linearity of PRT. 6 7. Appendix: o C Ω 100.00 100.39 100.78 101.17 101.56 101.95 102.34 102.73 103.12 103.51 103.90 104.29 104.68 105.07 105.46 105.85 106.24 106.63 107.02 107.40 107.79 o C Ω 108.18 108.57 108.96 109.35 109.73 110.12 110.51 110.90 111.29 111.67 111.67 112.06 112.83 113.22 113.61 114.00 114.38 114.77 115.15 115.54 o C Ω 115.93 116.31 116.70 117.08 117.47 117.86 118.24 118.63 119.01 119.40 119.78 120.17 120.55 120.93 121.32 121.71 122.09 122.47 122.86 123.24 o C Ω 123.63 124.01 124.39 124.77 125.16 125.54 125.93 126.31 126.69 127.07 127.46 127.84 128.22 128.61 128.99 129.37 129.75 130.13 130.52 130.90 o C Ω 131.28 131.66 132.04 132.42 132.80 133.18 133.57 133.95 134.32 134.71 135.09 135.47 135.85 136.23 136.61 136.99 137.37 137.75 138.13 138.51 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 7