thermocouple measurement value lower than actual value of causes

Thermocouple as a very common temperature measurement element, in the actual use process often encounter such a problem, that is, the data measured by thermocouple is smaller than the actual value, so what are the causes of this kind of failure?

1. Internal electrode leakage (local short circuit) of thermocouple;

Solution: take out the thermocouple electrode and check the cause of leakage. If it is caused by poor insulation of insulating pipe, it should be replaced;

2. The inside of thermocouple is wet;

Solution: take out the thermocouple electrode, dry the thermocouple protection tube and electrode separately, and check whether the protective tube has air leakage and water leakage, and replace the unqualified protection tube (which thermocouple protection tube has);

3. Deterioration or corrosion of thermoelectric electrode;

Solution: cut off the deteriorated part, re weld the working end, or replace with a new thermocouple;

4. Local short circuit of terminal in thermocouple junction box;

Solution: open the terminal box cover, clean the terminal, eliminate the cause of local short circuit, and cover the junction box tightly;

5. Local short circuit of compensation conductor;

Local short circuit or replacement of insulation;

6. The type configuration of compensation lead and thermocouple is wrong;

Solution: replace the compensation lead with thermocouple;

7. The polarity of compensation wire and thermoelectric pole is reversed;

Solution: re connect;

8. Improper installation position of thermocouple or insufficient insertion depth;

Solution: change the installation position or method and insertion depth;

9. The reference temperature of thermocouple is too high or the temperature of two contacts is different;

Solution: accurate temperature compensation of reference end;

10. The type of thermocouple is inconsistent with the index of instrument;

Solution: replace the thermocouple and compensation wire to make it consistent with the graduation mark of the measuring instrument;

11. The resistance of thermocouple circuit is too high;

Solution: adjust the resistance to meet the requirements;

12. The surface area of thermocouple protection tube is too much;

Solution: remove the thermocouple, clear the scale outside the protection tube;