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How to troubleshoot and repair thermocouple faults

2018-03-23 22:24:51

Thermocouples are widely used in industrial production and scientific research activities to detect and control temperature because of their simple structure, fast dynamic response, high measurement accuracy, wide measurement range and remote measurement. In the installation, the use of the process will inevitably appear this or that failure, Tianchang Huafen cable limited summed up the thermoelectric potential change, thermocouple no thermoelectric potential and instrument display instability of the three most common thermocouple failure phenomenon of the treatment method to share with you.

Tools/Materials
1

Vernier calipers

2

multimeter

Methods/Steps
1

The thermoelectric potential change of the thermocouple is mainly manifested in the output signal does not match the actual value. At this time, check whether the insertion length meets the on-site temperature measurement requirements (too long or too short); The installation position and installation method are appropriate; Whether the surface of the protective sleeve has accumulated dirt; Whether the interior is wet and leaking; Whether the electrode has shrinkage phenomenon; Measure whether the end solder joint is spherical, the surface is smooth, there are no air bubbles or slag inclusion; Whether the even filaments are discolored and metamorphic. Treatment method: 1. Take out the coupling wire, dry the protection and coupling wire separately (do not bake with fire). 2. Use vernier calipers to check the geometry of thermocouples, and replace those that do not meet the requirements. 3. If the solder joint is not spherical, the surface is uneven, there are no air bubbles or slag inclusion, cut off the solder joint and re-weld it, and use it after inspection. 4. Replace the new thermocouple if it deteriorates and discoloration. 5. Change the insertion length or installation position to the best measurement requirements.

2

Second, no thermoelectric potential thermocouple No thermoelectric potential is popular to say that the thermocouple is broken, mainly as the instrument shows the maximum value or remains in place, at this time should check whether the internal wire short circuit. The broken wire may be caused by mechanical damage to the electrode or deterioration of the thermocouple at high temperature for a long time. Treatment method: 1. If the coupling wire is lost or broken, the solder joint can be re-welded, and the installation can be used after the inspection is qualified (the length of re-welding will be shorter, pay attention to the change of insertion length!) . 2. If the damage is serious or the couple wire deteriorated, the new thermocouple should be replaced in time and the original thermocouple scrapped.

3

In the case that the display instrument has been tested without fault, the display value of the instrument is floating, and it should be checked whether the thermocouple terminal and the thermocouple wire are in good contact; Whether the thermocouple is securely installed; Whether the thermocouple oscillates; Whether there is conductive liquid, wet dust and metal impurities at the thermocouple joint; Whether the electrode is grounded, short-circuited or disconnected; Whether the connection with the instrument is firm; Whether the thermocouple wire seems to be broken, not broken, poor welding. 1. Clean the junction box of the thermocouple and install it firmly after drying. 2. Re-weld the thermocouple and use it after passing the test.3. Use a multimeter to measure the resistance value of the thermocouple wire, and replace it if it fails. 4. Find out where the thermocouple compensation wire is grounded, short circuited, and broken, and repair or replace the new compensation wire.

4

Thermocouple troubleshooting and maintenance is probably the first to say these common. In addition, due to negligence caused by human faults, such as the index number and the instrument do not match, the thermocouple compensation wire and the thermocouple type does not match, the thermocouple compensation wire and the thermocouple polarity reverse connection, improper insertion length, etc., the thermocouple output is larger or smaller than the actual value, resulting in high or low display value of the instrument. The handling methods of these faults are relatively simple, as long as you strengthen the sense of responsibility, usually learn more relevant knowledge, read and understand the instructions in detail during actual operation, and install the thermocouple correctly according to the installation specifications and instrument requirements. It can effectively reduce or avoid thermocouple failures.

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