PURPOSE: To minimize the dispersion of the output voltage due to the uneven characteristics of the integrated circuit, by inserting the variable resistance between the positive pole of the power source and the thermocouple and thus securing the control for the bias voltage which is applied to the input negative pole terminal of the operational amplifier.

CONSTITUTION: Fixed resistance R0 and variable resistance VR1 are inserted between the positive pole (+) of the power source and thermocouple terminal TH in the circuit which uses the single power source and carries out amplification of the heat electromotive force of the thermocouple for the temperature control. As a result, the offset voltage can be increased and decreased artificially through the control of resistance VR1 although some characteristics dispersion may exist in integrated circuit IC1 for amplifier.