How do thermocouples and thermal resistances work?

1. When a thermocouple has two different conductors or semiconductors A and B forming a loop, and its two ends are connected to each other, as long as the temperature at the two junctions is different, the temperature at one end is T, which is called the working end or the hot end, and the other The temperature at one end is T0, which is called the free end (also called the reference end) or cold end. An electromotive force will be generated in the circuit. The direction and magnitude of the electromotive force are related to the conductor material and the temperature of the two junctions. This phenomenon is called the 'thermoelectric effect2. Thermal resistance The temperature measurement principle of thermal resistance is based on the characteristic that the resistance value of conductor or semiconductor changes with temperature to measure temperature and temperature-related parameters. Thermal resistors are mostly made of pure metal materials. At present, platinum and copper are widely used, and materials such as nickel, manganese and rhodium have been used to make thermal resistors. Thermal resistance usually needs to transmit the resistance signal to the computer control device or other secondary instruments through the lead. Extended information: the difference between thermocouple and thermal resistance: 1. On-site judgment during work The thermocouple has positive and negative poles, and the compensation wires also have positive and negative points. First of all, ensure that the connection and configuration are correct. During operation. The common ones are short circuit, open circuit, poor contact (can be judged by a multimeter) and deterioration (identified according to the surface color). When checking, separate the thermocouple from the secondary meter, use a tool to short-circuit the compensation wire on the secondary meter, the meter indicates room temperature and then short-circuit the thermocouple terminal, the meter indicates the ambient temperature where the thermocouple is located (no, the compensation wire has Failure), and then use the mv file of the multimeter to roughly estimate the thermoelectric potential of the thermocouple (if normal, please check the process). The thermal resistance short circuit and open circuit can be judged with a multimeter. During operation, if a short circuit is suspected, just remove the end of the resistance and look at the display instrument. The meter value shows low or unstable, the possibility of water in the protection tube is very large, and the thermal resistance open circuit shows a small short circuit. Second, from the point of view of the material, thermal resistance is a metal material, a metal material with temperature-sensitive changes, and a thermocouple is a bimetallic material, which is two different metals. Due to temperature changes, the two different metal wires A potential difference is generated at the end. 3. The temperature ranges detected by the two sensors are different. The thermal resistance generally detects the temperature range of 0-150 degrees (of course it can detect negative temperatures), and the thermocouple can detect the temperature range of 0-1000 degrees (or even higher). Therefore, the former is Low temperature detection, the latter is high temperature detection.

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