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Thermocouple is a commonly used temperature measuring element in temperature measuring instruments. When the two ends of two conductors with different components are connected to form a loop, when the temperatures of the two junction thermocouples are different, a thermal current will be generated in the loop. If there is a temperature difference between the working end of the thermocouple and the reference end, the display instrument will indicate the temperature value corresponding to the thermoelectric potential generated by the thermocouple. The thermoelectric heat of the thermocouple will increase as the temperature of the measuring end increases. Its size is only related to the thermocouple material and the temperature at both ends, and has nothing to do with the length and diameter of the hot electrode. The shapes of various thermocouples are often very different due to needs, but their basic structures are roughly the same. They usually consist of main parts such as hot electrodes, insulating sheath protection tubes and junction boxes. They are usually used in conjunction with display instruments, recording instruments and electronic regulators. Features: 1. High measurement accuracy. Because the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium. 2. Wide measurement range. Commonly used thermocouples can continuously measure from -50 to 1600°C. Some special thermocouples can measure as low as -269°C (such as gold, iron, nickel and chromium) and as high as 2800°C (such as tungsten-rhenium). 3. Simple structure and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size or opening. They have protective sleeves on the outside, making them very convenient to use. type: Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The standard thermocouple referred to is * * The standard stipulates the relationship between thermoelectric potential and temperature, the allowable error, and a thermocouple with a unified standard scale. It has a matching display instrument for selection. Non-standardized thermocouples are not as good as standardized thermocouples in terms of use range or order of magnitude. They generally do not have a unified graduation table and are mainly used for measurements in certain special occasions. Standardized Thermocouples In China, since January 1, 1988, all thermocouples and thermal resistors have been produced in accordance with IEC international standards, and seven types of standardized thermocouples, S, B, E, K, R, J, and T, have been designated as unified design thermocouples in my country. Structural form of thermocouple In order to ensure that the thermocouple works reliably and stably, its structural requirements are as follows: 1. The two hot electrodes that make up the thermocouple must be welded firmly. ； 2. The two hot electrodes should be well insulated from each other to prevent short circuit ； 3. The connection between the compensation wire and the free end of the thermocouple must be convenient and reliable. ； 4. The protective sleeve should be able to ensure that the hot electrode is fully isolated from harmful media. According to different temperature measurement environments and different usage methods, thermocouples are divided into two categories: assembled thermocouples and armored thermocouples. As a transmitter for measuring temperature, industrial assembled thermocouples are usually used in conjunction with display instruments, recording instruments and electronic regulators. It can directly measure the surface temperature of liquid, steam and gas media and solids ranging from 0℃ to 1800℃ in various production processes.