Cold end compensation principle of temperature transmitter thermocouple

Thermocouples are commonly used temperature measuring components in temperature measuring instruments. They directly measure temperature and convert the temperature signal into a thermoelectric potential signal, which is then converted into the temperature of the measured medium through electrical instruments (secondary instruments). The appearance of various thermocouples is often very different due to needs, but their basic structures are roughly the same. They are usually composed of temperature transmitters such as hot electrodes, insulation sleeves, and junction boxes. They are usually used in conjunction with display instruments, recording instruments, and electronic regulators.
When measuring temperature with a thermocouple, it is required that the temperature of its cold end (the measuring end is the hot end, and the end connected to the measuring circuit through a lead is called the cold end) remains constant, so that the magnitude of its thermoelectric potential is proportional to the measured temperature. If the temperature changes at the cold end during measurement, it will seriously affect the accuracy of the measurement. Taking certain measures to compensate for the impact caused by temperature changes at the cold end is called cold end compensation of thermocouples.
The cold end compensation of thermocouples usually uses a bridge composed of a thermistor connected in series at the cold end. The three arms of the bridge are standard resistors, and the other arm is composed of a (copper) thermistor. When the temperature at the cold end changes (such as increasing), the thermoelectric potential generated by the thermocouple will also change (decrease), and at this time, the resistance value of the thermoelectric resistor in the series bridge will also change, causing the voltage at both ends of the bridge to change (increase). If the parameters are well selected and the wiring is correct, the voltage generated by the bridge is exactly equal to the amount of change in thermoelectric potential with temperature, and the total output voltage (potential) of the entire thermocouple measurement circuit accurately reflects the measured temperature value. This is the cold end compensation principle of temperature transmitter thermocouple.
Thermocouple thermometer is currently the most widely used type of thermometer. A thermocouple thermometer is a temperature measuring instrument that usually consists of a thermocouple, a thermocouple cold junction temperature compensation device (or component), and a display instrument, which are connected by wires. How is the compensation for the cold end of thermocouple temperature measurement calculated
The law of intermediate temperature refers to the fact that the thermoelectric potential between two junctions (at temperatures T and T0) in a thermocouple circuit is equal to the algebraic sum of the thermoelectric potential at temperatures T and Tn and the thermoelectric potential at temperatures Tn and T0. Tn refers to the intermediate temperature.
Application of the law of intermediate temperature: When the cold end temperature is not 0 degrees Celsius, the actual thermoelectric potential E (t, t0) of the known circuit cannot be directly used to find the temperature value of the hot end by looking up the table. It is even more unacceptable to use the actual thermoelectric potential E (t, t0) of a known circuit to directly look up the temperature value from a table, and then add the cold end temperature value to determine the measured temperature value at the hot end. Instead, it is necessary to make corrections according to the law of intermediate temperature.
Thermocouple temperature measurement and cold junction compensation calculation method can be summarized in one sentence: "Sum up first, then check the table to obtain the temperature".