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The judgment of the actual service life of fabricated thermocouples must be made through long-term collection
2012-4-7 9:18:34

输入产生故障判别法: 1. Method for judging faults caused by assembled thermocouple input:
1) After wiring correctly according to the meter wiring diagram, the meter first displays the thermocouple graduation number of the meter, and then displays the range of the meter. Then the digital tube at the bottom of the meter displays the set temperature, and the digital tube at the top of the meter displays the measured temperature. . If the upper digital tube displays the temperature of the heating body instead of "OVER", "0000" or "000", it indicates that the input part of the meter is faulty, and the following checks should be made: A) Remove the thermocouple from the meter thermocouple Remove the input terminal, and then short the input terminal of the instrument thermocouple with any wire. When the power is turned on, when the value displayed on the upper digital tube is about room temperature, it means that the internal wiring of the thermocouple is open and the thermocouple of the same type should be replaced. If it is still the condition mentioned above, it means that the input terminal of the instrument is damaged during transportation, and the instrument must be replaced. B) Remove the thermocouple of the above faulty instrument and replace it with the thermocouple connected to the same indexing instrument that runs normally. After power on, when the digital tube on the original faulty instrument displays the temperature of the heating element, the thermocouple is described. The internal wiring is open. Replace the thermocouple of the same type. If it is still the condition mentioned above, it means that the input terminal of the instrument is damaged during the transportation of the instrument and the instrument must be replaced. C) Remove the faulty thermocouple from the instrument, use a multimeter to measure the ohm (R) * 1 position, and use the two multimeter rods to measure the two ends of the thermocouple. If the resistance displayed on the multimeter is very large, explain The internal connection of the thermocouple is open. Replace the thermocouple of the same type. Otherwise, there is a certain resistance value, indicating that there is a problem with the input terminal of the instrument, and the instrument should be replaced. 2) The wiring is correct according to the wiring diagram of the meter. If the meter has a negative value after the meter is powered on, it means that the thermocouple “+” and “-” connected to the meter are connected incorrectly. Just redo it. 3) The wiring is correct. When the meter is running, the temperature displayed on the top of the digital tube differs from the actual measured temperature by 30 & ordm; C ~ 60 & ordm; C. Even the difference is larger, indicating that the graduation number of the meter and the graduation number of the thermocouple are wrong. According to the corresponding relationship between the thermocouple temperature (& ordm; C) and the millivolt (MV) value of the thermocouple graduation number B, S, K, E, etc., the same temperature (& ordm; C), The volt value (MV) B is the smallest, the S is the smallest, the K is the largest, and the E is the largest. The service life of a thermocouple is related to its deterioration. The so-called degradation of a thermocouple means that it deteriorates after it is used. Thermocouples made of metals or alloys have internal grains that gradually grow at high temperatures. At the same time, the alloy contains a small amount of impurities, and its position or shape will also change, and it will also react to reducing or oxidizing gases in the surrounding environment. With the above changes, the thermoelectromotive force of the thermocouple will also change extremely sensitively. Therefore, deterioration of the thermocouple is inevitable.

的使用寿命:热电偶的劣化是一个量变过程,对其定量很困难,将随热电偶的种类﹑直径﹑使用温度﹑气氛﹑时间的不同而变化。 Service life of fabricated thermocouples : The deterioration of thermocouples is a quantitative process, and it is difficult to quantify them. It will vary with the type, diameter, operating temperature, atmosphere, and time of the thermocouple. The service life of a thermocouple refers to the time during which the deterioration of the thermocouple exceeds the allowable error, and even the disconnection cannot be used. Only the stability of thermocouples is required in our standards. That is to say, the change of thermoelectromotive force before and after use at a certain temperature for 200h. However, no service life has been found. Japan's requirements for the service life of thermocouples are based on the continuous use time of thermocouples specified in the Japanese JIS (C-1602-1995) standard. For B, R, S thermocouples, 2000h, K, E, J, T thermocouples are 10,000h. In actual use, assembled thermocouples usually have protective tubes, and bare wires are used only in special cases. Therefore, in most cases, the life of the protective tube determines the life of the thermocouple. The judgment of the actual service life of a thermocouple must be based on long-term collection and accumulation of data under actual use conditions, in order to give a more accurate result.


是科研﹑生产最常用的温度传感器,虽然结构简单,但是,使用中不注意仍然会产生较大测量误差。 Assembled thermocouple is the most commonly used temperature sensor for scientific research and production. Although the structure is simple, careless use will still cause large measurement errors. The author discusses in detail the choice of temperature measurement points, the main causes of errors in the insertion depth, response time, thermal radiation, and thermal impedance of thermocouples, and points out the thermocouple heterogeneity, the use of the atmosphere Insulation resistance, K-type thermocouple selective oxidation, K-state and shunt error of armored thermocouple, etc. It is helpful to improve the measurement accuracy and extend the service life of the thermocouple.