Centigrade_thermometer_with_cold_junction_compensation

Published:2009/7/24 3:08:00 Author:Jessie | From:SeekIC

Fig. 13-40 This circuit is an electronic thermometer with a 10 mV/℃ output from 0℃ to 1300℃. To trim, first short out the LM329B, the LM335 and the thermocouple. Measure and record the output voltage from A1 (this should be equal to the input offset voltage of A1 times the voltage gain). Remove the short from the thermocouple and apply a 50-mV input to A1 and adjust the 5-kΩ gain potentiometer until the A1 output voltage is 12.25 V above the previously recorded value. Short out the thermocouple again, but remove the short across the LM335. Adjust the 10-kΩ TC potentiometer so that the output voltage from A1 equals 10 mV/°K times the absolute temperature. Finally, remove the short across the LM329B and adjust the 10-kΩ zero potentiometer so that the A1 output voltage equals 10 mV/℃ times the ambient temperature in 0℃. The table of Fig. 13-40B shows the error resulting from thermocouple nonlinearity as a function of temperature. National Semiconductor Linear Applications Handbook 1991, p. 524, 525.



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