Thermocouple circuit with open circuit detection facility, uses high frequency signals to check continuity, which do not interfere with correct operation of thermocouple

摘要

The thermocouple (3) is connected via thermocouple connection wires (31, 32) to the inputs of a chopper amplifier (1). The chopper amplifier has a clock output (13) which feeds a high frequency signal to the thermocouple via a buffer circuit (4) and a capacitor (5). The signal passes through the junction (3) and another capacitor (6) to a detector (20). If the signal is not detected, because of a short circuit, the detector clamps one of the inputs of the amplifier (1).