Temperature compensation of thermocouple cold end?

A basic requirement for using thermocouples to measure temperature is that the temperature value of one endpoint must be known. If the temperature at that end can be maintained at 0 ℃, then based on the measured thermoelectric potential, the temperature value at the other end can be directly obtained by referring to the calibration table. This temperature fixed end is often referred to as the reference end.

In theory, thermocouples are measured at the cold end with 0 ℃ as the standard. However, the instrument is usually at room temperature during measurement, but due to the cold end not being at 0 ℃, the thermoelectric potential difference decreases, resulting in inaccurate measurements and errors. Therefore, the compensation measure taken to reduce errors is cold end temperature compensation.

Temperature compensation of thermocouple cold end

Due to the fact that the materials of thermocouples are generally expensive (especially when using precious metals), and the distance between the temperature measuring point and the instrument is far, in order to save thermocouple materials and reduce costs, compensation wires are usually used to extend the cold end (free end) of the thermocouple to a temperature stable control room and connect it to the instrument terminals.

It must be pointed out that the function of the thermocouple compensation wire is only to extend the thermoelectric electrode and move the cold end of the thermocouple to the instrument terminal in the control room. It cannot eliminate the influence of temperature changes at the cold end on temperature measurement and does not have a compensation effect. Therefore, other correction methods need to be used to compensate for the impact of cold end temperature t0 ≠ 0 ℃ on temperature measurement.

When using thermocouple compensation wires, attention must be paid to model matching, polarity cannot be connected incorrectly, and the temperature at the connection end between the compensation wire and the thermocouple cannot exceed 100 ℃.