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The principle of thermocouple temperature sensor

The thermocouple temperature sensor is a contact temperature sensor and also a pyroelectric temperature sensor. The temperature of a physical quantity is converted into an electric potential signal, which is relatively weak and belongs to a millivolt-level electric potential signal. Finally, a temperature control instrument or transmitter must be equipped to realize temperature measurement and temperature signal conversion. The principle is very simple, the basic principle is the thermoelectric effect. If two conductors of different materials are connected end to end, as long as the temperatures of the two nodes are different, a thermoelectric potential can be generated in this loop and a thermoelectric current is formed, which is the thermoelectric effect.

A formed thermocouple has only one node welded, which is its working end or measuring end, also called the hot end. The unsoldered end is the connection point, called the free end or reference end, also called the cold end. therefore. As long as the temperature difference between the hot end and the cold end is greater, the output thermoelectric potential is greater. If you connect a digital multimeter in series in the loop, you can clearly see that the potential is constantly changing.

　　 As mentioned above, two conductors of different materials are connected end to end. When the two conductors are in contact, the electrons in the conductor will diffuse. Also, because the free electron density in the conductor is different, the free electron density in the conductor will diffuse to the conductor with the low electron density. As a result, the high density of free electrons in the conductor loses electrons and carries a positive potential, and the diffused free electron conductor is obtained and carries a negative potential. When the diffusion reaches dynamic equilibrium, a potential difference is formed in the loop, that is, contact electromotive force. It can be seen that the higher the temperature of the working end, the more intense the diffusion of free electrons in the conductor, and the higher the potential difference in the loop when a new dynamic equilibrium is reached. In general, the total electromotive force of the thermocouple is not only related to the free electron density in the conductor, but also related to the temperature of the two nodes, and the free electron density in the conductor depends on the characteristics of the conductor material.