What is the working principle of thermocouples?

The working principle of thermocouple (thermocouple principle) What is a thermocouple? This starts with the principle of thermocouple temperature measurement. Thermocouple is a kind of temperature sensing element, it is a primary instrument, it directly measures temperature, and converts the temperature signal into thermoelectromotive force signal, which is converted into The temperature of the measured medium. The basic principle of thermocouple temperature measurement is that two different components of material conductors form a closed loop. When there is a temperature gradient at both ends, current will flow through the loop. At this time, there is Seebeck electromotive force-thermoelectromotive force between the two ends. This is the so-called Seebeck effect. Two homogeneous conductors with different compositions are thermoelectrodes, the end with a higher temperature is the working end, the end with a lower temperature is the free end, and the free end is usually at a certain constant temperature. According to the functional relationship between thermoelectromotive force and temperature, a thermocouple index table is made; the index table is obtained when the free end temperature is at 0℃, and different thermocouples have different index tables. When the third metal material is connected in the thermocouple circuit, as long as the temperature of the two junctions of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal in the circuit. Therefore, when the thermocouple measures the temperature, it can be connected to the measuring instrument, and after the thermoelectromotive force is measured, the temperature of the measured medium can be known. B: The working principle of thermocouples: Two conductors with different components (called thermocouple wires or thermoelectrodes) are connected at both ends to form a loop. When the temperature of the junction is different, an electromotive force will be generated in the loop. This phenomenon is called It is the thermoelectric effect, and this electromotive force is called thermoelectric force. Thermocouples use this principle for temperature measurement. The end directly used to measure the temperature of the medium is called the working end (also called the measuring end), and the other end is called the cold end (also called the compensation end); the cold end and the display When the meter or supporting meter is connected, the display meter will point out the thermoelectric potential generated by the thermocouple. A thermocouple is actually a kind of energy converter, which converts heat energy into electrical energy, and uses the generated thermoelectric potential to measure the temperature. For the thermoelectric potential of the thermocouple, you should pay attention to the following issues: 1: The thermoelectric potential of the thermocouple is thermoelectric The difference of the temperature function between the two ends of the couple, not the function of the temperature difference between the two ends of the thermocouple; 2: The size of the thermoelectric potential generated by the thermocouple. When the material of the thermocouple is uniform, it has nothing to do with the length and diameter of the thermocouple. It is related to the composition of the thermocouple material and the temperature difference between the two ends; 3: When the composition of the two thermocouple wires of the thermocouple is determined, the thermoelectric potential of the thermocouple is only related to the temperature difference of the thermocouple; if the temperature of the cold junction of the thermocouple Keep it constant, the thermoelectric potential of this thermocouple is only a single-valued function of the working end temperature. The thermocouple utilizes a closed circuit composed of two different materials; when the temperature of the two ends is different, a current will be generated; and then through the measuring instrument, the temperature of the medium can be easily obtained. Commonly used thermocouple materials are: thermocouple indexing number thermoelectrode material positive electrode S platinum rhodium 10 pure platinum R platinum rhodium 13 pure platinum B platinum rhodium 30 platinum rhodium 6K nickel chromium nickel silicon T pure copper copper nickel J iron copper nickel N Nickel chromium silicon nickel silicon E nickel chromium copper nickel

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