K-type thermocouple main temperature measurement principle

- Jul 09, 2019-

The thermocouple temperature measurement must be composed of three parts: thermocouple, connecting wire and display instrument.

 

Thermocouple core and temperature measuring filament 1 composed of K-type thermocouple. If the hot end of the thermocouple is heated so that the temperatures at both ends of the cold and the heat are different, a thermoelectric potential is generated in the thermocouple circuit. The physical phenomenon is called the thermoelectric phenomenon (ie, the thermoelectric effect). The potential generated in the thermocouple loop consists of a temperature difference potential and a contact potential. Contact potential: It is a thermoelectric potential generated when two conductors with different electron densities are in contact with each other. When two different conductors A and B are in contact, assuming that the electron densities of conductors A and B are Na and Nb, respectively, and Na>Nb, the diffusion ratio of electrons in both directions is not at the contact surface of the two conductors. Similarly, the number of electrons diffused from the conductor A to the conductor B is larger than the number of electrons diffused from B to A. Conductor A loses electrons and is positively charged, and conductor B acquires electrons and is negatively charged. Therefore, an electrostatic field from A to B is formed on the contact faces of the two conductors A and B. This electric field will hinder the continuation of the diffusion motion and accelerate the movement of electrons in the opposite direction, increasing the number of electrons from B to A. Finally reached the state of dynamic balance. At this time, a potential difference is also formed between A and B. This potential difference is called the contact potential. This potential is only related to the temperature at which the two conductors are in contact with each other. When the materials of the two conductors are constant, the contact potential is only related to the junction temperature. The higher the temperature, the more active the electrons in the conductor, the more electrons diffuse from the A conductor to the B conductor, and the greater the electromotive force generated at the contact surface, ie, the greater the contact potential.