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What is the difference between thermocouple and thermal resistance?

Author: 316 views Time: April 17, 2020

Summary of information:

Thermocouple and thermal resistance are commonly used in industrial production of temperature measurement instruments, their use may be relatively similar, but their working principle and scope of use are not the same, the following from Jiangsu Huanya electric heating instrument Co., Ltd. to explain the difference between thermocouple and thermal resistance.


  

 

At present, there is a standard specification for thermocouples in the world. It is stipulated that the thermocouples are divided into eight different divisions, namely B, R, s, K, N, e, J and t. the lower can measure - 270 ℃ below zero, and the higher can reach 1800 ℃. Among them, B, R and s belong to platinum series thermocouples, So they're called noble metal thermocouples, and the rest are called cheap metal thermocouples.



There are two types of thermocouple structure, common type and armored type.

The ordinary thermocouple is generally composed of thermal electrode, insulating tube, protective sleeve and junction box, while armored thermocouple is a solid combination of thermocouple wire, insulating material and metal protective sleeve after being assembled and stretched. But the electrical signal of thermocouple needs a special wire to transmit, which we call compensation wire.

Different thermocouples need different compensation wires, and its main function is to connect with the thermocouple, so that the reference end of the thermocouple is far away from the power supply, so that the temperature of the reference end is stable.



There are two types of compensation type

The chemical composition of the extension wire is the same as that of the compensated thermocouple. However, in practice, the extended wire is not made of the same material as the thermocouple, and the wire with the same electronic density as the thermocouple is generally used instead. The connection between the compensation wire and the thermocouple is generally very clear. The positive pole of the thermocouple is connected with the red line of the compensation wire, and the negative pole is connected with the remaining color.



Copper nickel alloy is usually used as the material of general compensating wire.


Thermocouple is the most widely used temperature device in temperature measurement. Its main characteristics are wide temperature measurement range, stable performance, simple structure and good dynamic response. In addition, the conversion transmitter can transmit 4-20mA current signal remotely, which is convenient for automatic control and centralized control.



The temperature measurement principle of thermocouple is based on thermoelectric effect. Two different conductors or semiconductors are connected to form a closed circuit. When the temperature at the two contacts is different, the thermoelectric potential will be generated in the circuit. This phenomenon is called thermoelectric effect, also known as Seebeck effect. The thermoelectric potential generated in a closed loop consists of two kinds of potentials: thermoelectric potential and contact potential.



Although thermal resistance is widely used in industry, its application is limited due to its temperature measurement range. The principle of thermal resistance temperature measurement is based on the characteristic that the resistance value of conductor or semiconductor changes with temperature. It also has many advantages, such as remote transmission of electrical signals, high sensitivity, strong stability, good interchangeability and accuracy, but it needs power supply excitation and can not measure the temperature change instantaneously.



The temperature measured by the industrial thermal resistance is relatively low, and the temperature measurement does not need compensation wire, and the price is relatively cheap.

We have been consulting about the difference between the thermoelectric instrument and the thermoelectric instrument in Jiangsu for 20 years.


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