Thermocouple in use after a period of time, there will be wear and tear, and may even damage, generally the stand or fall of thermocouple and thermocouple wire in it ( Silk) , but how to judge the stand or fall of thermocouple. How to judge the stand or fall of thermocouple: first determine the appearance of the thermocouple wire is no problem, it is good or bad, have to go through testing to determine. Will stay thermocouple wire wear measurement thermocouple special porcelain sleeve, with standard platinum-rhodium thermocouple in the tube furnace, the hot side insert tube furnace in a porous soaking with metal in the cylinder made of nickel. Put their compensation the cold end of the wire in the ice water to keep zero degrees Celsius in the container. Hold the tube furnace at the high allowable temperature of the thermocouple, and keep the stable range. This time use after testing qualified, hui sten potentiometer, measure standard thermocouple and under test thermocouple thermoelectric potential difference and record. According to the records of thermoelectric potential difference, check grade table find out their corresponding temperature, if the thermocouple out-of-tolerance under test, can be judged to be unqualified.