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Common Troubleshooting Methods for Thermocouples

Thermocouple is widely used in industrial production and scientific research activities to detect and control temperature because of its simple structure, fast dynamic response, high measurement accuracy, wide measurement range, and can be used for long-distance measurement. Thermocouple in the installation, work in the process of use will inevitably appear one or another failure.

The following on the thermocouple processing methods and common failures such as processing and peer discussion, exchange.

1. The Potential Than The Actual Value Of Low (Instrument Indication Low)

1. thermocouple electrode deterioration or moldy working end.

Troubleshooting method: cut off the deteriorated part, re-weld the working end or replace the new electrode.

2. Thermocouple internal moisture leakage.

Troubleshooting methods: remove the hot electrode, the hot electrode, insulating porcelain tube drying, and check the leakage of the protection tube, the failure should be re-welded or replaced with a new protection tube.

3. thermocouple junction box terminals ask too much dust or iron chips short circuit.

Troubleshooting method: use a brush to remove dust, remove iron filings, the junction box sealed. The junction box should be down the wire hole, to prevent poor sealing and make the water, dust and dirt into the junction box.

4. thermocouple temperature measurement circuit resistance value greater than 15 ohms.

Troubleshooting method: Use a multimeter to test the circuit resistance, should meet the requirements of 15 ohms.

5. compensation wire moisture short circuit.

Troubleshooting methods: the compensation wire and the protection tube between the water clean, eliminate the short contact, replace the new compensation wire, take waterproof, anti-short circuit measures.

6 compensation wire type and thermocouple indexing inconsistent.

Troubleshooting method: replace the compensation wire with thermocouple matching.

7. thermocouple installation position is not appropriate, shallow insertion depth.

Troubleshooting methods: select the appropriate installation position, adjust the insertion depth. General requirements will be installed as far as possible over the working end of the center of the pipe about 5-10mm, thermocouple insertion depth should not be less than its own protection tube diameter 8 ~ times, otherwise, should be added to expand the tube.

8. The temperature of the cold end of the thermocouple is too high.

Troubleshooting method: the cold end of the thermocouple with compensation wire moved to a lower temperature and more constant occasions.


2. The Potential Is Higher Than The Actual Value (Instrument Indication Is High)

1. electric couples and instrument indexing inconsistent.

Troubleshooting method: replace the thermocouple, so that it is consistent with the instrument.

2. thermocouple and compensation wire does not match.

Troubleshooting method: replace the thermocouple consistent compensation wire.

3. thermocouple installation position is not appropriate.

Troubleshooting methods: select the appropriate installation location.

3. The Thermocouple Potential Output, But Not Stable

1. thermocouple terminals and hot electrode poor contact.

Troubleshooting methods: the terminal block and thermal electrode reference end wipe clean, re-tighten.

2. thermocouple temperature measurement circuit part of the insulation is damaged, causing intermittent short circuit or grounding phenomenon.

Troubleshooting method: find the fault point, repair the insulation.

3. thermocouple is not firmly installed or external vibration.

Troubleshooting method: the thermocouple needs to be reinstalled firmly or take vibration reduction measures.

4. external interference.

Troubleshooting method: find out the interference after shielding or grounding. Prohibit the thermocouple leads and power cable installed in the same conduit.


4. The Thermocouple No Thermal Potential Output

1. short circuit in the measurement line.

Troubleshooting methods: re-insulate the short circuit or replace the new couples.

2. measurement circuit disconnection.

Troubleshooting methods: use a multimeter segmentation check to find the break, reconnect the line.

3. Loose wiring poles.

Troubleshooting method: just tighten the terminal.

4. thermocouple burned off.

Troubleshooting method: re-weld or replace the thermocouple with a new one.

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