The working principle of thermocouples in electric heaters: Two conductors with different compositions (called thermocouple wires or thermoelectric electrodes) are connected at both ends to form a circuit. When the temperature of the junction drops changes, an electromotive force occurs in the circuit, which is called the thermoelectric effect, and this electromotive force is called the thermoelectric electromotive force; Thermocouples use this principle for temperature measurement, and the end directly used for measuring the temperature of the medium is called the operating end and the other end is called the cold end; The cold end is connected to the visible surface or matching surface, and the visible surface will indicate the thermoelectric force generated by the thermocouple. A thermocouple is actually an energy converter that converts thermal energy into electrical energy and measures temperature using the generated electromotive force. Regarding the electromotive force of a thermocouple, the following issues should be noted: 1. The electromotive force of a thermocouple is the difference in temperature function between the two ends of the thermocouple, not a function of temperature difference between the two ends of the thermocouple; 2. The magnitude of the electromotive force generated by a thermocouple is not related to the length and diameter of the thermocouple, but rather to the composition of the thermocouple and the temperature difference between the two ends, when the data of the thermocouple is uniform; 3. When the composition of the two thermocouple wires is determined, the magnitude of the thermocouple electromotive force is only related to the temperature difference of the thermocouple; If the temperature at the cold end of the thermocouple persists, the electromotive force of the thermocouple is only a single value function of the temperature at the operating end. What is a thermocouple? This starts with the principle of thermocouple temperature measurement: a thermocouple is a temperature sensing element, which is an external surface that can directly measure the temperature, convert the temperature signal into a thermoelectric electromotive force signal, and convert it into the temperature of the measured medium through the electrical surface. The basic principle of thermocouple temperature measurement is that it is a closed circuit composed of two different components of raw material conductors; When there is a temperature gradient at both ends, there is a current passing through the circuit, and there is a Seebeck electromotive force - thermoelectric electromotive force - between the two ends, which is known as the Seebeck effect. Two homogeneous conductors with different compositions are thermoelectric electrodes, with the higher end being the operating end and the lower end being the free end. The free end is generally at a stable temperature. Based on the functional relationship between thermoelectric electromotive force and temperature, create a thermocouple calibration table; The graduation table is obtained at a temperature of 0 degree , and different thermocouples have different graduation tables. When connecting the third metal data in the thermocouple circuit, as long as the temperature of the two contacts is the same, the electromotive force generated by the thermocouple will remain unchanged, that is, not affected by the connection of the third metal in the circuit. Therefore, when using thermocouples for temperature measurement, the measuring surface can be connected, and after measuring the thermoelectric electromotive force, the temperature of the measured medium can be known as the drop electric heater.