Principle of thermocouple compensation wire in general, thermocouple temperature measurement table could be dozens of meters, thermocouple cold end ( The outlet end) Temperature and the temperature measurement table different ambient temperature ( Even up to dozens of degrees) 。 If using ordinary copper wire, according to the principle of thermocouple, wiring place and produce thermoelectric potential, can produce error of measurement. If the compensating conductor ( Must be compatible and thermocouple dividing Numbers) , it chooses the metal materials, can produce wiring temperature potential of as small as possible, as far as possible, reduce the temperature measurement error. That is to say, the thermocouple cold end will be moved to the temperature measurement table. Long-distance transmission wire pressure drop, because temperature measurement table high input impedance, potential of thermocouple temperature difference ( Millivolt level) Transfer current ( Micro grade A) Small, wire on the pressure drop loss is very small, in the general case, within the error range. So have a thermocouple transmitter, thermocouple signal input and output 4 - 20 ma, so can't compensation wire, can long-distance transmission.