Armored thermal resistance is a simple introduction and classification

Armored thermocouples and thermal resistors are all contact-type temperature measurements in temperature measurements. Although the same effect is used to measure the temperature of objects, their principles and characteristics are different.

First, introduce the thermocouple, thermocouple is the most widely used temperature measurement temperature device, his main feature is a wide temperature range, the performance is relatively stable, while the structure is simple, dynamic response is good, more able to remotely transmit 4-20mA Signals for automatic control and centralized control. Thermocouple temperature measurement principle is based on the thermoelectric effect. Connecting two different conductors or semiconductors into a closed loop, when the temperature at two junctions is different, a thermoelectric potential will be generated in the loop. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect. The thermoelectric potential generated in a closed loop has two potential components: a thermoelectric potential and a contact potential. Thermoelectric potential refers to the potential generated at the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so the potentials they generate are also different. The contact potential, as the name implies, means that two different conductors are in contact. Because their electron densities are different, they produce a certain amount of electron diffusion. When they reach a certain equilibrium, the potential formed depends on the material properties of the two different conductors and the temperature of their contact points.

   At present, thermocouples used in the world have a standard specification. Internationally, thermocouples are divided into eight different divisions, namely B, R, S, K, N, E, J, and T. The lowest measurement temperature is available. Zero under 270 °C, up to 1800 °C, of ​​which B, R, S platinum series of thermocouples, because platinum is a precious metal, so they are also known as the precious metal thermocouple and the remaining few are called cheap metal thermoelectric I.

There are two types of thermocouples, common type and armor type. General thermocouples are generally composed of hot electrodes, insulating tubes, protective sleeves and terminal boxes, while armored thermocouples are assembled by combining thermocouple wires, insulating materials and metal protective sleeves. Extensive processing of a solid combination. But the electric signal of the thermocouple needs a kind of special wire to transmit, this kind of wire is called compensating wire. Different thermocouples require different compensation wires. Their main function is to connect with the thermocouple and keep the reference end of the thermocouple away from the power supply, so that the reference junction temperature is stable.

Compensation wire is divided into compensation type and extension type. The chemical composition of the extension wire is the same as that of the compensated thermocouple. However, in practice, the extension wire is not the same material as the thermocouple. Generally, the heat wire is used. Even the wires with the same electron density are replaced. The wire of the compensation wire and the thermocouple is generally very clear. The positive pole of the thermocouple connects the red wire of the compensation wire, and the negative pole connects the remaining colors. Most of the material of the general compensation wire is copper-nickel alloy.

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