Working principle and internal structure analysis of thermocouple

Thermocouples are one of the most commonly used temperature sensing elements in the industry. Its advantages are: ① high measurement accuracy. Because the thermocouple directly touches the measured object, it is not affected by the central medium. ②The measurement scale is wide. Commonly used thermocouples can be continuously measured from -50 to +1600 °C, and some special thermocouples can measure as low as -269 °C (such as gold-iron-nickel-chromium) and as high as +2800 °C (such as tungsten-rhenium). ③The structure is simple and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size and initial, and have a protective sleeve outside, which is very convenient to use. 1. The basic principle of thermocouple temperature measurement is to weld two conductors or semiconductors A and B of different materials to form a closed loop. When there is a temperature difference between the two sticking points 1 and 2 of the conductors A and B, an electromotive force occurs between the two, thus forming a large current in the loop, which is called the thermoelectric effect. Thermocouples use this effect to work. 2. Varieties and structural composition of thermocouples (1) Varieties of thermocouples Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The standard thermocouple referred to refers to the thermocouple whose thermoelectric potential and temperature, the allowable error, and the consistent standard graduation table are regulated by the national standard. Non-standardized thermocouples are not as good as standardized thermocouples in terms of scale or order of magnitude, and generally do not have a consistent indexing table, which is mainly used for measurement in some special occasions. Standardized thermocouple China Since January 1, 1988, all thermocouples and thermal resistances are produced in accordance with IEC international standards, and seven standardized thermoelectric Even for China's consistent planning thermocouple. (2) The structure of the thermocouple In order to ensure the reliable and stable operation of the thermocouple, its structure requirements are as follows: ① The welding of the two hot electrodes constituting the thermocouple must be firm; ② The two hot electrodes should be polarized between each other. Good insulation to prevent short circuit; ③ The connection between the compensation wire and the free end of the thermocouple should be convenient and reliable; ④ The protective sleeve should be able to ensure sufficient isolation of the thermode from the harmful medium.

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