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Thermocouple working principle

Two different conductors (called thermocouple wires or hot electrodes) are joined at both ends into a loop.

When the temperatures of the two junctions are different, an electromotive force is generated in the loop. This phenomenon is called a thermoelectric effect, and this electromotive force is called a thermoelectric potential. Thermocouples use this principle for temperature measurement. The one that is directly used to measure the temperature of the medium is called the working end (also called the measuring end), the other end is called the cold end (also called the compensating end); the cold end and the display The instrument or supporting instrument is connected, and the display meter indicates the thermoelectric potential generated by the thermocouple.

 

A thermocouple is actually an energy converter that converts thermal energy into electrical energy and measures the temperature with the generated thermoelectric potential. For the thermoelectric potential of a thermocouple, the following problems should be noted:

1. The thermoelectric potential of the thermocouple is the difference between the temperature functions at both ends of the working end of the thermocouple, not the function of the temperature difference between the cold end and the working end of the thermocouple;

2. The magnitude of the thermoelectric potential generated by the thermocouple, when the material of the thermocouple is uniform, is independent of the length and diameter of the thermocouple, and is only related to the composition of the thermocouple material and the temperature difference between the two ends;

3. When the composition of the two thermocouple wires of the thermocouple is determined, the thermocouple potential of the thermocouple is only related to the temperature difference of the thermocouple; if the temperature of the cold junction of the thermocouple is kept constant, the thermoelectric potential of the thermocouple is only A single-valued function of the working temperature. Conductors or semiconductors A and B of two different materials are welded together to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between the two, and thus the loop A current of one size is formed, which is called a thermoelectric effect. Thermocouples use this effect to work.

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