In a certain temperature range with matching thermocouple thermal electromotive force of nominally the same pair of wires called compensation wire. They are used to connect the thermocouple and the measuring device to compensate for the error caused by the temperature change at the connection between them and the thermocouple. The compensation wire is divided into two types: extension type and compensation type due to the different alloy materials of the core wire. 1. Compensation type wire: the chemical composition of the alloy wire is different from that of the thermocouple wire, but its thermoelectric potential value is the same as that of the thermocouple, and "C" is used to indicate the compensation type. Examples: SC, KC, etc. 2. Extended compensation wire: the chemical composition and thermoelectric potential of the alloy wire are the same as those of the thermocouple wire. The extended form is indicated by "X. Example: KX, TX, etc. Line.