Introduce basic thermocouple
the basic principle of thermocouple temperature measurement are two different components of the material of conductor closed loop, when the temperature gradient is at both ends, the loop will have an electric current passes through, the existed between the electromotive force on both ends thermoelectric emf, this is the so-called seebeck effect ( 塞贝克效应) 。 Two different components of homogeneous conductor electrode as heat, the temperature is higher for work at the end of the end, one end of the low temperature as the free end, usually free end under a constant temperature. According to the thermoelectric emf as a function of temperature, the thermocouple indexing table; Indexing table is free end temperature at 0 ℃, under the condition of different thermocouples with different indexing table.
in the thermocouple circuit connected to the third kind of metal material, the two contacts at the same temperature as long as the material, produced by the thermocouple thermoelectric is set to remain the same, which is not affected by the third metal access in the loop. Therefore, when the thermocouple temperature measurement, can be connected to the measuring instrument, measured after the thermoelectric emfs, can know the temperature of the measured medium. Thermocouple measuring temperature to the cold end ( Measure the end for the hot end, by the end of the lead connected to the measurement circuit is called cold junction) Temperature remains constant, the size of thermoelectric potential and measured temperature in certain proportion relationship. When measuring, the cold end ( Environment) Temperature changes, will seriously affect the accuracy of measurement. Take action at the cold end compensation due to the impact of the cold end temperature change is called the thermocouple cold junction compensation is normal. Connected to the measuring instrument with special compensation conductor.
thermocouple cold junction compensation calculation method:
from millivolt to temperature: measuring the cold end temperature, the conversion for the corresponding millivolt values, millivolt values with thermocouple, the temperature conversion;
from the temperature to the millivolt: measure the actual temperature and the cold end temperature, the conversion of millivolt values respectively, after subtracting the millivolt values, quick temperature.