一、1. What is a thermocouple?

Thermocouples are one of the most commonly used temperature sensing components in the industry. The principle of thermocouple operation is based on the Seeb effect, in which two conductors of different compositions are connected in a loop. If the temperature of the two junction ends is different, it is in the loop. A physical phenomenon in which a thermal current occurs.

A thermocouple is a temperature sensing component that is an external appearance. It directly measures the temperature and converts the temperature signal into a thermoelectromotive force signal, and then converts it into the temperature of the measured medium through an electrical appearance (secondary appearance).

The basic principle of thermocouple temperature measurement is that the material conductors of two different compositions form a closed loop. When there is a temperature gradient at both ends, there will be current passing through the loop. At this moment, there is an electromotive force between the two ends - the thermoelectromotive force, which is called The Seebeck effect.

The homogeneous conductor of two different components is a hot electrode, the higher temperature end is the working end, the lower temperature end is the free end, and the free end is generally at a constant temperature. According to the thermoelectromotive force as a function of temperature, a thermocouple indexing table is made; the indexing table is obtained under the condition that the temperature at the end is 0 °C, and different thermocouples have different indexing tables.

When the third metal data is connected to the thermocouple loop, only the temperature of the two contacts of the data is the same, and the thermoelectric potential generated by the thermocouple will remain unchanged, that is, not affected by the third metal access loop. . Therefore, when the thermocouple is measuring temperature, it can be connected to the measuring surface. After measuring the thermoelectromotive force, the temperature of the measured medium can be known.

When there is a temperature difference between the two attachment points 1 and 2 of the conductors A and B, an electromotive force occurs between the two, and a large current is formed in the loop. This phenomenon is called a thermoelectric effect. Thermocouples use this effect to work.

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

1: The thermoelectric potential of the thermocouple is the difference between the temperature functions of the two thermocouples, not the temperature difference between the two thermocouples;

2: The size of the thermoelectric potential generated by the thermocouple, when the data 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 data and the temperature difference between the two ends;

3: When the thermocouple wire data components of the thermocouple are determined, the thermoelectric 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 operating temperature.