Thermocouple is a kind of temperature sensor is commonly used in the thermal element, has simple structure, stable performance, wide temperature range, temperature measurement precision, convenient use, etc, are widely used in machinery industry production, scientific research in the aspects of heat treatment temperature and temperature control program. But in use process, because of the influence of the interference factors, makes the thermocouple failure problem, affect the production run smoothly. Thermocouple failure reason and processing method: failure: thermoelectric potential is smaller than the actual value. Cause analysis: ( 1) Short circuit. ( 2) Short circuit between thermocouple junction box inside the terminal. ( 3) Compensation wire short circuit because of insulation burn out. ( 4) Compensation conductor don't match with thermocouple. ( 5) Compensation conductor and thermocouple reverse polarity. ( 6) Insert depth and the installation location is wrong. ( 7) Thermocouple cold junction temperature is too high. Processing method: 1) On checking if caused by moisture, drying; If the insulation fault of the porcelain tube, it should be replaced. ( 2) Open the box, the wiring scrub brush clean. ( 3) The insulation or replace a new compensation conductor should be short circuit. ( 4) Replacement of the same type into compensation conductor. ( 5) To meet the right. ( 6) Change the installation location and insertion depth. ( 7) Thermocouple wires for compensation wire, turn away the cold end of drier. Second, the failure phenomenon: thermoelectric potential is bigger than actual. Cause analysis: ( 1) Compensation cables with thermocouple type does not match. ( 2) Insert depth or installation location is wrong. ( 3) Hot electrode metamorphism. ( 4) The jamming signal enters. ( 5) The thermocouple reference end temperature on the high side. Processing method: 1) Replacement of the same type of compensating conductor. ( 2) Change the installation location or insert depth. ( 3) Replace the thermocouple. ( 4) Check for interference sources, and eliminated. ( 5) Adjust the reference temperature or amended. 3, fault phenomenon: measuring instrument is not stable,, high low. Cause analysis: ( 1) Poor contact thermal electrodes in terminal. ( 2) Thermocouple with intermittent short circuit or intermittent grounding phenomenon. ( 3) Hot electrode has been broken or seems broken off. ( 4) Thermocouple installation is solid, swing. （ 5) Compensation conductor grounding or intermittent short circuit phenomenon. Processing method: 1) Then good again. ( 2) Remove thermal electrode from the protection tube of thermocouples, find out the fault point and eliminated. ( 3) Replace the new electrode. ( 4) Installation is firm. ( 5) Find out the fault point and eliminated. Four, fault phenomenon: thermocouple potential error. Cause analysis: ( 1) Hot electrode metamorphism. ( 2) Improper installation location and installation of thermocouple method. ( 3) The surface of the thermocouple protection tube fouling too much. ( 4) Measure short circuit ( Thermocouple and compensating conductor) 。 ( 5) Thermocouple circuit disconnection. ( 6) Terminal is loose. Processing method: 1) Replace the thermocouple. ( 2) Change the installation location and installation method. ( 3) To clean up. ( 4) Replace the insulation will be short circuit. ( 5) Find the disconnection, and reconnect. ( 6) Tighten the terminal.