What is the calculation correction method for thermocouples?

Since the temperature-thermoelectric potential curve (thermocouple graduation table) of the thermocouple is obtained when the cold end temperature is kept at 0℃, and the instrument used with it is scaled according to this relationship curve, even if the compensation wire is used to extend the cold end of the thermocouple to a place with constant temperature, as long as the cold end temperature is not 0℃, the indication value of the instrument must be corrected.
If the hot end temperature of the temperature measuring thermocouple is T, and the cold end temperature is Tn instead of 0℃, the output potential of the thermocouple is measured to be E(T, Tn), and the thermoelectric potential when the hot end temperature is T and the cold end is 0℃ is calculated according to the intermediate temperature law E(T, 0℃) = E(T, Tn) + E(Tn, 0℃), and then the hot end temperature T is found from the graduation table. It should be noted that due to the nonlinearity of the thermocouple temperature potential curve, the addition mentioned above is the addition of thermoelectric potential, not a simple temperature addition.
For example: when measuring temperature with a nickel-chromium-nickel-silicon thermocouple, the cold end temperature of the thermocouple is Tn = 30°C, and the thermoelectric potential E(T, Tn) = 40.347 mV when the cold end is 30°C is measured. The thermoelectric potential E(Tn, 0°C) = 1.203 mV is found from the scale table when the hot end is 30°C and the cold end is 0°C. Then E(T, O) = E(T, Tn) + E(T, O) = (40.347 + 1.203) mV = 41.55 mV, and T = 1010°C is also found from the scale table.
Thermocouples are sensors that measure temperature based on the thermoelectric effect and are commonly used temperature measuring elements in temperature measuring instruments. The appearance of various thermocouples is often very different due to needs, but their basic structure is roughly the same. They are usually composed of main parts such as thermoelectrodes, insulating sleeve protection tubes and junction boxes, and are usually used in conjunction with display instruments, recording instruments and electronic regulators.
The basic principle of thermocouple temperature measurement is that two conductors of different materials form a closed loop. When there is a temperature gradient at both ends, current will pass through the loop. At this time, there is an electromotive force between the two ends - thermoelectric electromotive force, which is the so-called Seebeck effect. Two homogeneous conductors of different components are thermocouples. 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. According to the functional relationship between thermoelectric electromotive force and temperature, a thermocouple scale is made; the scale is obtained when the temperature of the free end is 0℃, and different thermocouples have different scales.
The thermoelectric characteristics of thermocouples refer to the phenomenon that an electric potential difference is generated on the contact surface of two metals at a certain temperature.
1. The size of the thermocouple loop property is only related to the property of the material and the temperature at both ends, and has nothing to do with the length and thickness of the thermocouple.
2. Only conductors of two different properties can form a thermocouple; when the temperatures at both ends of the thermocouple are different, a thermoelectric potential will be generated.
3. After the material is determined, the magnitude of the thermoelectric potential is only related to the temperature at both ends of the thermocouple.