The difference between thermocouple and thermal resistance:
Although they are all contact temperature measuring instruments, their temperature measuring ranges are different.
Thermocouples are used in high temperature environments, because their output thermoelectric potential is very small when they are in the middle and low temperature regions. When the potential is small, anti-interference measures and secondary table sum requirements are very high, otherwise the measurement will be inaccurate. In the low temperature region, the relative error caused by the change of the cold end temperature and the change of the ambient temperature is very prominent, and it is not easy to obtain full compensation.
At this time, at medium and low temperatures, the temperature measurement range of thermal resistance is generally 200~500 ℃, and even lower temperatures can be measured (for example, a low temperature of about 1K can be measured with carbon resistance). Now the platinum thermal resistance Pt100 is used normally. . (There is also Pt50, copper resistance is also used in industry, but the temperature measurement range is small, between 150 ~ 150 ℃. In some special occasions, there are indium resistance, manganese resistance, etc.).
Wear-resistant and high-temperature thermocouple
Temperature measurement principle:
The basic principle of thermocouples to measure temperature is the thermoelectric effect, and the secondary meter is a voltmeter or an electronic potentiometer to improve accuracy.
The resistance works based on the characteristic that the resistance value of conductors and semiconductors changes with temperature, and the secondary meter is an unbalanced bridge.
On-the-spot judgment at work.
1. Thermocouple. The thermocouple has positive and negative poles, and the compensation wire also has positive and negative points. First, ensure that the connection is correct and the configuration is correct. During operation, common short-circuit, open-circuit, poor contact (with a multimeter can be judged) and deterioration (according to surface color to identify). When checking, separate the thermocouple from the secondary meter.
2. Thermal resistance. It is nothing more than short circuit and open circuit. It can be judged with a multimeter. During operation. If a short circuit is suspected, just remove a wire end from the resistance end and see the display meter. If it reaches the maximum value, the thermal resistance is short circuited. Back to zero, the wire is shorted. When ensuring normal connection and configuration, the meter value shows low or unstable, and the protection tube may be flooded. Display maximum, thermal resistance open circuit. Display minimum, short circuit.
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