Fixed screw type thermocouple

Fixed screw type thermocouple

Thermocouple (thermocouple) is a temperature measuring element commonly used in temperature measuring instruments. It directly measures the temperature, converts the temperature signal into a thermoelectromotive force signal, and converts it into the temperature of the measured medium through an electrical instrument (secondary instrument). The appearance of various thermocouples is often very different due to needs, but their basic structures are roughly the same, usually composed of main parts such as thermode, insulating sleeve protection tube and junction box, usually with display instruments, recording instruments and electronic adjustment. used in conjunction with the device.

Temperature measurement conditions of Fixed screw type thermocouple

It is a kind of temperature sensing element and a primary instrument. The thermocouple directly measures the temperature. The closed circuit composed of two conductors with different components and materials produces electron diffusion due to different materials and different electron densities. After stable equilibrium, the potential is generated. When there is a gradient temperature at both ends, there will be current in the circuit, generating thermoelectric EMF. The greater the temperature difference, the greater the current will be. The temperature value can be known after measuring the thermoelectric EMF. Thermocouple is actually an energy converter, which can convert heat energy into electric energy.

Technical advantages of thermocouples: the thermocouple has a wide temperature measurement range and relatively stable performance; The measurement accuracy is high, and the thermocouple is in direct contact with the measured object, which is not affected by the intermediate medium; The thermal response time is fast, and the thermocouple responds flexibly to temperature changes; The measurement range is large, and the thermocouple can measure temperature continuously from -40~+ 1600 ℃; The thermocouple has reliable performance and good mechanical strength. Long service life and convenient installation.

The electric couple must be composed of two conductor (or semiconductor) materials with different properties but meeting certain requirements. There must be a temperature difference between the measuring end and the reference end of the thermocouple.

The conductors or semiconductors A and B of two different materials are welded together to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, electromotive force is generated between them, so a large and small current is formed in the circuit. This phenomenon is called thermoelectric effect. Thermocouples use this effect to work.

Main features editing and broadcasting of Fixed screw type thermocouple
1. Simple assembly and convenient replacement;
2. Spring loaded temperature sensing element with good seismic performance;
3. High measurement accuracy;
4. Large measurement range (-200 ℃ ~ 1300 ℃, under special circumstances -270 ℃ ~ 2800 ℃);
5. Fast thermal response time;
6. High mechanical strength and good pressure resistance;
7. High temperature resistance up to 2800 degrees;
8. Long service life.

Structure requirements
In order to ensure the reliable and stable operation of the thermocouple, the structural requirements of the thermocouple are as follows:
1. The welding of the two thermoelectrodes constituting the thermocouple must be firm;
2. The two thermoelectric poles should be well insulated from each other to prevent short circuit;
3. The connection between the compensation wire and the free end of the thermocouple should be convenient and reliable;
4. The protective sleeve shall be able to ensure that the Thermoelectrode is fully isolated from harmful media.

Working principle
Two conductors with different components (called thermocouple wires or thermoelectrodes) are connected at both ends to form a circuit. When the temperature of the two junction points is different, electromotive force will be generated in the circuit. This phenomenon is called thermoelectric effect, and this electromotive force is called thermal electromotive force. Thermocouples use this principle to measure the temperature. The end directly used to measure the medium temperature is called the working end (also known as the measuring end), and the other end is called the cold end (also known as the compensation end); The cold end is connected with the display instrument or supporting instrument, and the display instrument will indicate the thermoelectric potential generated by the thermocouple.

Thermocouple is actually an energy converter, which converts heat energy into electric energy and measures temperature with the generated thermoelectric potential. For the thermoelectric potential of thermocouple, the following problems should be paid attention to:

1. The thermoelectric potential of the thermocouple is the difference of the temperature function at both ends of the working end of the thermocouple, not the function of the temperature difference between the cold end and the working end of the thermocouple;

2. When the thermocouple material is uniform, the thermoelectric potential generated by the thermocouple has nothing to do with the length and diameter of the thermocouple, but only with the composition of the thermocouple material and the temperature difference at both ends;

3. When the material composition of the two thermocouple wires of the thermocouple is determined, the thermal potential of the thermocouple is only related to the temperature difference of the thermocouple; If the temperature of the cold end of the thermocouple remains constant, the thermoelectric potential of the thermocouple is only a single value function of the working end temperature. The conductors or semiconductors A and B of two different materials are welded together to form a closed loop, as shown in the figure. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, electromotive force is generated between them, thus forming a large and small current in the circuit. Thermocouples use this effect to work.