The basic working principle of a thermocouple is the thermoelectric effect: two metal conductors or semiconductors with different components are connected together to form a closed loop. When the temperature of the two connection points a and b is different, the loop will An electromotive force will be generated to form a thermal current phenomenon.

When a thermocouple is used, the hot end is placed in the material or environment to be tested, and the cold end is placed outside the production equipment. If the temperatures at both ends are different, a thermoelectric potential will be generated in the thermocouple circuit. There is a one-to-one relationship between the thermoelectric potential of the thermocouple and the temperature, and the relevant data is listed in a table, which is called a thermocouple index table. After measuring the thermoelectric potential of the thermocouple with a temperature measuring instrument, the temperature of the measured object can be known.

Different cold junctions have great interference to the measurement results. Therefore, in the industry, the method of compensating wires is often used to eliminate similar errors.

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