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Since thermocouples produce small amounts of millivoltage
for any given temperature, a precision millivoltmeter can be used to
test the output signal from all types of thermocouples. The temperature
at the tip of the thermocouple must be controlled while the millivoltage
measurement is made. Since the thermocouple sends the transmitter a millivolt
signal, a precision millivolt power supply could be used for transmitter
calibration. Manufacturers have combined the voltmeter and power supply
into one tester. This tester has the tables for millivolt signal strength and the cold-junction compensation built into it so the technician only
needs to select the type of thermocouple and the temperature range, and the test circuit will provide an accurate reading from this. When the
transmitter is being calibrated, the tester can send the voltage signal
for the minimum and maximum ranges of each type of thermocouple.
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