The thermoelectric corner compensates the action of the wire

For example: For example, K division number thermocouple, composed of (nickel chromium, nickel silicon), if connected to the copper wire, will produce (nickel chromium, copper, nickel silicon), (nickel chromium, nickel silicon) three thermocouples, the first two are not general thermocouples, three thermocouples temperature difference potential (can be positive, can be negative) algebraic sum, that is, to reach the thermometer wire at the electromotive force, the electromotive force indicated by the temperature, Plus the instrument's room temperature compensation of 20 ° C, is the displayed value.

If the thermocouple has a copper material at one end, the thermoelectric potential corresponding to 780 ° C at the thermometer should be displayed at 800 ° C, as indicated in the question.

When using the thermocouple compensation wire, you must pay attention to the model match, the polarity can not be connected wrong, and the temperature of the compensation wire and the thermocouple connection can not exceed 100℃. If the temperature measurement accuracy requirements are not high, the temperature difference between the thermocouple terminal and the instrument end is not large, ordinary copper wire can be used.

The composition of the two wires is different

Because "the compensation wire of the thermocouple is a pair of wires with an insulating layer that has the same nominal value of the thermoelectric motive force of the matched thermocouple within a certain temperature range (including room temperature 0℃), it can constitute a thermocouple within a certain range (in fact, the compensation wire and the same index thermocouple are the same material), According to the middle conductor law of thermocouples, "Access the middle conductor (third conductor) in the thermocouple circuit as long as the temperature at both ends of the middle conductor is the same, the introduction of the middle conductor has no effect on the total potential of the thermocouple circuit." That is, without considering the influence of the thermocouple, the compensation wire can also generate a thermoelectric potential, which is equal to the temperature difference potential between the tail end of the thermocouple and the measuring device.

When used correctly, the potential of the thermocouple and the potential of the compensation wire are superimposed, in the case of constant temperature at the hot and cold ends, with the temperature change at the connection between the thermocouple and the compensation wire, the temperature difference potential of the thermocouple increases, and the temperature difference potential of the compensation wire decreases, and vice versa, to compensate the impact of the temperature change between the thermocouple and the measuring device. The measuring device measures the superposition of the thermoelectric potential generated by the thermocouple and the compensating potential generated by the compensating wire.