Thermocouple introduction

When there is a temperature difference between the two attachment points 1 and 2 of conductor a and B, the electromotive force will be generated between them, thus forming a large current in the circuit. This phenomenon is called thermoelectric effect. It's the so-called Seebeck effect. The thermocouple / probe works with this effect.

Conductors A and B are called thermoelectric poles. The higher temperature end (T) is called the working end (usually welded together); the lower temperature end (to) is called the free end (usually at a constant temperature).

According to the relationship between thermoelectric potential and temperature function. It can be made into thermocouple graduation table. The index table is obtained under the condition of free end temperature to = 00C. Different thermocouples have different graduations.

When the third metal material is connected into the thermocouple circuit, as long as the temperature of two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal in the circuit. Therefore, when the thermocouple is used for temperature measurement, the temperature of the measured medium can be known after the thermoelectric potential is measured by the measuring instrument.

Theoretically, any two kinds of conductors can be made into thermocouples, but in fact, not all materials can make thermocouples. Therefore, the thermoelectric materials must meet the following requirements:

(1) thermocouple material can produce higher thermoelectric potential under the action of temperature, and the relationship between thermoelectric potential and temperature is preferably linear or approximately linear single value function;

(2) it can measure higher temperature and be used in a wide temperature range in China. After long-term use, its physical, chemical properties and thermoelectric properties are stable;

(3) the resistance temperature coefficient of the material should be small, the resistivity should be high, the conductivity should be good, and the heat capacity should be small;

(4) the reproducibility should be good for mass production and interchangeability, so as to make a unified index table;

(5) good mechanical properties and even materials;

(6) rich resources and low prices.