# Level and Flow Measurement

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# Thermocouple working principle and principle structure

##### Author:Source:Date: 2021-05-26 14:03:26
1. Working principle

Two conductors of different compositions (called thermocouple wires or hot electrodes) are connected at both ends to form a loop. When the temperature of the two nodes is different, an electromotive force will be generated in the loop. This phenomenon is called pyroelectric effect, and this electromotive force is called thermoelectric force. Thermocouples use this principle to measure temperature. One end is directly used to measure the temperature of the medium, called the working end (also called the measuring end), and the other end is called the cold junction (also called the compensation end). The cold junction is connected to a display instrument or a supporting instrument, and the display instrument will indicate the thermoelectric potential generated by the thermocouple.

2. Basic structure

The basic principle of temperature measurement is that two conductors of different components form a closed loop. When there is a temperature gradient at both ends, there will be a current flowing through the loop, and there will be an EMF between the two ends—the thermoelectric EMF, which is the so-called Seebeck effect (SeebeckEffect). Two homogeneous conductors with different compositions are thermoelectrodes. The higher the temperature of the working end, the lower the temperature of the free end, and the free end is usually at a constant temperature. According to the functional relationship between thermoelectromotive force and temperature, the thermocouple scale is obtained when the free end temperature is 0℃, and different thermocouples have different scales.

3. Performance related to principles

9a6663f5

1. Simple assembly and convenient replacement

2. Spring temperature sensing element, good seismic performance

3. High measurement accuracy

4. Wide measuring range (-200 C~1300℃, special case -270 C~2800℃)

5. Fast thermal response time

6. High mechanical strength and good pressure resistance

7. High temperature resistance to 2800 degrees

8. Long service life.

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