How to know if the thermocouple is damaged or good

- Oct 09, 2020-

How to know if the thermocouple is damaged or good

 

1. Visually observe whether the protective tube is corroded and penetrated, whether it is leaking, etc.

2. Use a multimeter to measure the continuity. The resistance of the assembled thermocouple is generally not more than 2 ohms, and the resistance of the network cable is generally not more than 50 ohms. Generally greater than 1K can be determined to be broken.

3. Use a multimeter to measure the resistance value. Resistance over 100K is bad.

4. Use the multimeter ohm measurement method to measure, adjust the resistance, connect both ends, and burn it with a lighter. If the pointer of the multimeter is obviously larger or smaller, it means it is good. If the pointer does not move, it means it is broken.

5. Use a multimeter to measure the voltage at both ends in the millivolt range. If there is no voltage, it will be broken.

6. Remove the thermocouple from the thermocouple input end of the instrument, and then use any wire to short-circuit the thermocouple input end of the instrument. When the power is on, when the display value of the digital tube on the top of the meter is about room temperature, it means that the internal wiring of the thermocouple is open, and the thermocouple of the same type should be replaced. If it is still in the above-mentioned condition, it means that the input terminal of the instrument was damaged during transportation, and the instrument should be replaced.

7. Remove the thermocouple of the above-mentioned faulty instrument, and replace it with the thermocouple connected to the same kind of indexing instrument that is running normally next to it. After power on, when the digital tube on the original faulty instrument displays the temperature of the heating element, explain the thermocouple The connection is open and replace the thermocouple of the same type.

8. Remove the faulty thermocouple from the meter, use a multimeter to measure ohm (R) *1, use the two meter rods of the multimeter to measure the two ends of the thermocouple, if the resistance value displayed on the multimeter is very large, it means The internal connection of the thermocouple is open. Replace the thermocouple with the same type. Otherwise, there is a certain resistance value, indicating that there is a problem with the input end of the meter, and the meter should be replaced.

9. The wiring is correct according to the wiring diagram of the meter. If the digital tube on the meter displays a negative value after the meter is powered on, it means that the thermocouple "+" and "-" connected to the meter are connected incorrectly. Just change it again.

10. When the wiring is correct, when the meter is running, the temperature displayed by the digital tube on the meter differs from the actual measured temperature by 40 degrees to 70 degrees. The difference is even greater, indicating that the index number of the meter is wrong with the index number of the thermocouple. According to the thermocouple index number B, S, K, E and other thermocouple temperature corresponding to the millivolt (MV) value, at the same temperature, the generated millivolt value (MV) B index number is the smallest , S indexing number is the smallest, K indexing number is larger, E indexing number is the largest, according to this principle to judge.