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Working principle and structure of thermocouple1、 What is thermocouple
Thermocouple is one of the most commonly used temperature detection elements in industry. The operation principle of thermocouple is based on seeback effect, that is, two conductors with different components are connected into a circuit. If the temperature of two connecting ends is different, the physical phenomenon of thermal current occurs in the circuit. 2、 Basic principle of thermocouple temperature measurement Thermocouple is a kind of temperature sensing element, which measures the temperature directly, converts the temperature signal into thermoelectric EMF signal, and then converts the temperature of the measured medium through the electrical surface (two external surfaces). The basic principle of thermocouple temperature measurement is that two kinds of material conductors with different components form a closed circuit. When there is a temperature gradient at both ends, there will be current passing through the circuit. At this moment, there is an electromotive force - thermoelectric electromotive force between the two ends, which is the so-called Seebeck effect. Two kinds of homogeneous conductors with different components are thermoelectric poles, the one with higher temperature is the working end, the one with lower temperature is the free end, and the free end is generally at a constant temperature. According to the function relation between thermoelectric EMF and temperature, the graduation table of thermocouple is made. The graduation table is obtained when the end temperature is 0 ℃, and different thermocouples have different graduation tables. When the third metal data is connected to the thermocouple circuit, only if the temperature of the two contacts of the data is the same, the thermoelectric potential of the thermocouple will remain unchanged, that is, it will not be affected by the third metal in the circuit. Therefore, when the thermocouple is used for temperature measurement, it can be connected to the measuring surface, and the temperature of the measured medium can be known after the thermoelectric EMF is measured. When there is a temperature difference between two rigid points 1 and 2 of conductors A and B, electromotive force will occur between them, thus forming a huge and fine current in the circuit. This phenomenon is called thermoelectric effect. Thermocouples work with this effect. Two conductors with different components (called thermocouple wires or thermoelectric poles) are connected to a synthetic circuit. When the temperature of the junction is different, electromotive force will occur in the circuit. This phenomenon is called thermoelectric effect, and this electromotive force is called thermoelectric potential. The thermocouple uses this principle to measure the temperature. In this process, one end directly used to measure the temperature of the medium is called the working end (also known as the measuring end), and the other end is called the cold end (also known as the compensation end). The cold end is connected with the appearance or matching appearance, and the appearance will indicate the thermoelectric potential of the thermocouple. Thermocouple is actually a kind of energy converter, which converts heat energy into electrical energy, and measures the temperature with the generated thermoelectric potential. For the thermoelectric potential of thermocouple, the following problems should be paid attention to: 1: The thermoelectric potential of a thermocouple is a function of the temperature difference between the two ends of the thermocouple, not a function of the temperature difference between the two ends of the thermocouple; 2: When the data of thermocouple are uniform, the thermoelectric potential of thermocouple is not related to the length and diameter of thermocouple, but only to the composition of thermocouple data and the temperature difference between two ends; 3: When the data components of two thermocouple wires are determined, the thermoelectric potential of the thermocouple is only related to the temperature difference of the thermocouple; if the temperature of the cold end of the thermocouple is kept constant, the thermoelectric potential of the thermocouple is only a single value function of the temperature of the working end. |
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