How to Determine a Thermocouple Output Failure?

How to troubleshoot a Thermocouple?

1. After connecting the wires accurately according to the wiring diagram and powering on, the meter displays the thermocouple graduation firstly and then the range, measure the nixie tube on the lower part of the meter to display the setting temperature, and measure the nixie tube on the upper part of the meter to display the measuring temperature. If the upper nixie tube doesn’t display the temperature of the heating body but the other states such as “OVER”, “0000” or “000”, meaning that the output part of the meter goes wrong, following inspections shall be made:
   ① Remove the thermocouple from the thermocouple output end of the instrument and then short circuit the thermocouple output end of the instrument with a wire. If the temperature showed on the upper nixie tube is close to the room temperature after powering on, meaning that exterior wire connection of the thermocouple disconnects, replace with a same thermocouple. If it keeps a same state as previous, meaning that the output end of the instrument is damaged in transportation, change an instrument please.
   ② Remove the thermocouple from the above fault instrument and replace with the one from the normal operation instrument. If the upper nixie tube of the fault instrument displays the temperature of heating body, meaning that exterior wire connection of the thermocouple disconnects, replace with a same thermocouple. If it keeps a same state as previous, meaning that the output end of the instrument is damaged in transportation, change an instrument please.
   ③ Remove the thermocouple from the above fault instrument and measure its two ends with a multimeter at the (R)*1 position, if the multimeter shows a huge resistance value, meaning that exterior wire connection of the thermocouple disconnects, replace with a same thermocouple. Otherwise, there should be a certain resistance value, meaning that the output end of the instrument is damaged in transportation, change an instrument please.
2. Connect the wires accurately according to the wiring diagram, if the upper nixie tube shows a negative value after powering on, meaning that the positive and negative pole of the thermocouple are wrongly connected, change it please.
3. When the instrument is accurately connected, if the temperature displayed on the upper nixie tube has a difference of 30~60℃ or even larger with the actual measuring temperature, meaning that the graduations of instrument and thermocouple are wrongly set. According to the congruent relationship between the thermocouple temperature and MV value for different types of thermocouple graduation (such as B type, S type, K type, E type), the MV value of graduation B is the smallest in the same temperature, the graduation B is second smallest, graduation K is larger and graduation E is the largest, judge by this principle.