b) 
A researcher is considering which type of sensor to use to monitor the temperature inside a refrigerator which is kept at -70C. a) The thermocouple configuration as shown in Figure 3-1 is used to determine 11 (kept at the temperature of the refrigerator) and T2 is kept at 20C with copper and constantan being Mati and Mata respectively. Determine Vout. (5 MARKS) Mat T2 Copper T Mat Mat T2 TI Vout Mat Mat T2 T Mat T Copper An RTD has the temperature versus resistance characteristics given in Figure 3-2. Create an equation that relates the resistance reading to temperature with the reference temperature set at 20C. Indicate also the voltage reading that will be obtained when a 15mA constant current source is used to excite this RTD to measure the temperature of the refrigerator. (5 MARKS) C C C 2 C C C 0 10 20 30 40 200 210 220 230 240 250 260 800 810 820 830 840 850 375.51 378.48 381.45 384.40 387 34 390.26 60 -200 -190 -580 -170 - 160 - 150 -140 -130 -120 -110 -100 - 90 - 80 - 70 .60 270 280 18.49 22.80 27.08 31.32 35.53 39.71 43.87 48.00 52.11 56,19 60.25 64.30 68.33 72.33 76.33 80.31 84 27 88.22 92.16 96.09 70 80 90 100 110 120 130 140 150 160 170 180 190 100.00 103.90 107.79 111.67 115.54 119.40 123 24 127.07 130.89 134.70 138,50 142.29 146,06 149.82 153.58 157.31 161,04 164.76 168.46 172.16 175,84 179.51 183,17 186.82 190.45 194,07 197.69 201.29 204.88 208.45 212,02 215.57 219,12 222.65 226.17 229,67 233.17 236,65 240.13 243,59 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 290 300 310 320 330 340 350 360 370 380 390 247.04 250,48 253,90 257,32 260,72 264,11 267,49 270.86 274,22 277.56 280.90 284.22 287,53 290.83 294,11 297,39 300,65 303,91 307,15 310,38 600 610 620 630 640 650 660 670 680 690 700 710 720 730 740 750 760 770 780 790 313,59 316.80 319,99 323,18 326,35 329,51 332,66 335.79 338.92 342.03 345,13 348,22 351,30 354,37 357.42 360,47 363.50 366,52 369,53 372.52 . 50 - 40 560 . 30 - 20 - 10 570 580 590 Figure 3-2 A researcher is considering which type of sensor to use to monitor the temperature inside a refrigerator which is kept at -70C. a) The thermocouple configuration as shown in Figure 3-1 is used to determine 11 (kept at the temperature of the refrigerator) and T2 is kept at 20C with copper and constantan being Mati and Mata respectively. Determine Vout. (5 MARKS) Mat T2 Copper T Mat Mat T2 TI Vout Mat Mat T2 T Mat T Copper An RTD has the temperature versus resistance characteristics given in Figure 3-2. Create an equation that relates the resistance reading to temperature with the reference temperature set at 20C. Indicate also the voltage reading that will be obtained when a 15mA constant current source is used to excite this RTD to measure the temperature of the refrigerator. (5 MARKS) C C C 2 C C C 0 10 20 30 40 200 210 220 230 240 250 260 800 810 820 830 840 850 375.51 378.48 381.45 384.40 387 34 390.26 60 -200 -190 -580 -170 - 160 - 150 -140 -130 -120 -110 -100 - 90 - 80 - 70 .60 270 280 18.49 22.80 27.08 31.32 35.53 39.71 43.87 48.00 52.11 56,19 60.25 64.30 68.33 72.33 76.33 80.31 84 27 88.22 92.16 96.09 70 80 90 100 110 120 130 140 150 160 170 180 190 100.00 103.90 107.79 111.67 115.54 119.40 123 24 127.07 130.89 134.70 138,50 142.29 146,06 149.82 153.58 157.31 161,04 164.76 168.46 172.16 175,84 179.51 183,17 186.82 190.45 194,07 197.69 201.29 204.88 208.45 212,02 215.57 219,12 222.65 226.17 229,67 233.17 236,65 240.13 243,59 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 290 300 310 320 330 340 350 360 370 380 390 247.04 250,48 253,90 257,32 260,72 264,11 267,49 270.86 274,22 277.56 280.90 284.22 287,53 290.83 294,11 297,39 300,65 303,91 307,15 310,38 600 610 620 630 640 650 660 670 680 690 700 710 720 730 740 750 760 770 780 790 313,59 316.80 319,99 323,18 326,35 329,51 332,66 335.79 338.92 342.03 345,13 348,22 351,30 354,37 357.42 360,47 363.50 366,52 369,53 372.52 . 50 - 40 560 . 30 - 20 - 10 570 580 590 Figure 3-2
