Thermocouple temperature measurement principle
Galvanic temperature principle
The working mechanism of the thermocouple is based on the thermoelectric effect of the conductor. The two different metals A and B form a closed loop. When the two junction temperatures are different (T> T), the thermoelectric power Eab (T> T) is generated in the circuit. This phenomenon is called thermoelectric effect, as the picture shows. Among them, the T-side is called the hot end (working end), T. (A, B) is called the hot electrode. The size of the thermoelectric potential Eab (T, To) is determined by the contact potential of the two materials and the temperature difference potential of the single material. Contact potential
When the two different conductors of A and B are in close contact, since the internal free electron density N is different, let Na> Nb, so that the number of free electrons diffused from the conductor A to the conductor B per unit time is larger than that of the conductor B The number of electrons to the conductor A is large. Conductor A due to loss of electrons with a positive charge, the conductor B due to get a negative electrons, so that in the A, B contact to form a certain potential difference, known as the contact potential (Peltier potential), as shown. This potential will hinder the further diffusion of electrons. When the electron diffusion capacity is balanced with the resistance of the electric field, the electron diffusion at the contact reaches a dynamic equilibrium, and the contact potential also reaches a steady state value, which can be expressed as
Analysis of common problems of thermocouple and thermal resistance
1, because the thermocouple line and the compensation line is very strong, when we check, bad line, wire easy to loose, if there is such a temperature meter no display or more than set, the display is not allowed.
2, some mechanical easy to damage the front end of the thermocouple position, this time we should use the thermocouple material more wearable material.
3, usually we will reverse the line of the situation, it should be noted that if the temperature instrument display is not accurate, it is necessary to rule out whether the line reversed and so on.
4, thermocouple outside the layer is insulated, to thermocouple installed, maintenance, to minimize friction, so as not to break the ground insulation, usually this situation in the instrument display is generally low
