Working principle of thermocouple in electric heater: Two conductors of different compositions (called thermocouple wires or thermoelectrodes) are joined at both ends to form a circuit. When the temperatures at the junctions are different, an electromotive force is generated in the circuit. This phenomenon is called the thermoelectric effect, and the electromotive force is called thermoelectric potential. 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 compensating end). The cold end is connected to a display instrument or matching instrument, and the display instrument indicates the thermoelectric potential generated by the thermocouple.
A thermocouple is actually an energy converter that converts thermal energy into electrical energy, using the generated thermoelectric potential to measure temperature. Regarding the thermoelectric potential of a thermocouple, the following issues should be noted:
1: The thermoelectric potential of a thermocouple is a function of the temperature difference between the two ends, not a function of the temperature difference between the two ends;
2: When the thermocouple material is uniform, the magnitude of the thermoelectric potential generated is independent of the length and diameter of the thermocouple, and only depends on the composition of the thermocouple material and the temperature difference between the two ends;
3: Once the material composition of the two thermocouple wires is determined, the magnitude of the thermoelectric potential is only related to the temperature difference of the thermocouple; if the temperature of the cold end is kept constant, the thermoelectric potential of the thermocouple is a single-valued function of the working end temperature.
What is a thermocouple? This starts from the temperature measurement principle of thermocouples. A thermocouple is a temperature sensing element, a primary instrument, which directly measures temperature and converts the temperature signal into a thermoelectric potential signal, which is then converted into the temperature of the measured medium by an electrical instrument (secondary instrument).
Basic principle of thermocouple temperature measurement: Two conductors of different compositions form a closed loop. When there is a temperature gradient at the two ends, a current will flow through the loop, and a Seebeck electromotive force—thermoelectric potential—exists between the two ends. This is the so-called Seebeck effect. Two homogeneous conductors of different compositions are the thermoelectrodes. The end with higher temperature is the working end, and the end with lower temperature is the free end. The free end is usually at a constant temperature. Based on the functional relationship between thermoelectric potential and temperature, a thermocouple indexing table is made; the indexing table is obtained under the condition that the free end temperature is 0°C, and different thermocouples have different indexing tables. When a third metal material is inserted into the thermocouple circuit, as long as the temperatures at the two junctions of this material are the same, the thermoelectric potential generated by the thermocouple will remain unchanged, i.e., it is not affected by the insertion of the third metal into the circuit. Therefore, during thermocouple temperature measurement, a measuring instrument can be connected. After measuring the thermoelectric potential, the temperature of the measured medium can be known.electric heater.
