The basic principle of thermocouple temperature measurement is composed of two different components of the material composition of the closed loop conductor, when there is a temperature gradient at both ends, the circuit will have a current through, this time between the two sides there is electromotive force - thermal EMF, which The so-called Seebeck effect (Seebeck effect). Two different components of the homogeneous conductor for the hot electrode, the higher the temperature end of the work side, the lower end of the temperature free end, the free end is usually at a constant temperature. According to the thermoelectromotive force and temperature as a function of the thermocouple indexing table; table is the free end temperature at 0 ℃ under the conditions obtained, different thermocouples with different indexing table.

In the thermocouple circuit access to a third metal material, as long as the temperature of the two contacts the same material, thermocouple thermoelectric power generated by the same will remain unchanged, that is not affected by the third metal access circuit. Therefore, the thermocouple temperature, can access the measuring instrument, measured thermoelectromotive force, you can know the measured medium temperature. Thermocouple temperature required to measure the cold side (measurement side of the hot side, through the lead wire and the measurement circuit connected to the end of the cold side) as the temperature remains unchanged, the size of its thermoelectric power was measured with a certain proportion of temperature. If measured, the cold end of the (ambient) temperature changes, will seriously affect the measurement accuracy. In the cold end to take some measures to compensate for the cold junction temperature changes as the impact of the cold junction compensation as normal thermocouple. Dedicated compensation wire for connection to measuring instruments.

Thermocouple cold junction compensation calculation method:

From mV to temperature: measuring the cold side temperature, converted to the corresponding millivolt value, and the thermocouple millivolt value added, the conversion temperature;

From the temperature to mV: measured the actual temperature and the cold side temperature, respectively, converted to millivolt value, subtracted after the millivolt value, which was temperature