How to judge the quality of thermocouples? The correct selection method of thermocouples

How to judge the quality of thermocouples?

1. Visually observe whether the protective tube has corrosion, penetration, leakage, etc.

2. Use a multimeter to measure the conductivity. The resistance of the assembled thermocouple is generally not more than 2 ohms, and the resistance of the mesh wire is generally not more than 50 ohms. Generally, if it is greater than 1K, it can be determined that the thermocouple is damaged.

3. Use a multimeter to measure the resistance value. Resistance exceeding 100K is not good.

4. Measure with the multimeter ohm measurement method, adjust the resistance, connect the two ends, and burn it with a lighter. If the pointer of the multimeter becomes obviously larger or smaller, it means it should be 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 instrument thermocouple input terminal, and then short-circuit the instrument thermocouple input terminal with any wire. After the power is turned on, when the digital tube on the top of the instrument displays the value of 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 state, it means that the input terminal of the instrument is damaged during transportation, and the instrument should be replaced.

7. Remove the thermocouple of the above-mentioned faulty instrument and replace it with a thermocouple connected to the normal operation of the same type of graduated instrument next to it. After power is turned on, when the digital tube on the original faulty instrument displays the temperature of the heating element, it means that the thermocouple wiring is open, and the same type of thermocouple should be replaced.

8. Remove the faulty thermocouple from the instrument, measure ohm (R)*1 with a multimeter, and measure the two ends of the thermocouple with the two rods of the multimeter. If the resistance value displayed by the multimeter is large, it means that the internal connection of the thermocouple is open. Replace the same type of thermocouple. Otherwise, there is a certain resistance value, which means that there is a problem with the input end of the instrument, and the instrument should be replaced.

9. Connect the wires correctly according to the instrument wiring diagram. If the digital tube on the meter shows a negative value after the meter is powered on, it means that the thermocouples connected to the "+" and "-" terminals of the meter are connected incorrectly. Just change them again.