What are the issues with wear-resistant thermocouples?

1. The insulation layer of the compensating wire of the wear-resistant thermocouple was worn out, causing the signal circuit to be grounded. This is mainly because the compensating wire is relatively hard and not placed flat inside the junction box. When handling the fault, the junction box cover was twisted multiple times and the compensating wire was worn out. This type of fault is reflected in the temperature indication on the operator control station, which is generally lower.

2. The compensation wire of the wear-resistant thermocouple is reversed. This is mainly a problem that occurred during infrastructure construction, caused by the carelessness of the personnel responsible for wiring. It is considered a factor. When the compensation wire of the wear-resistant thermocouple is reversed, the display on the operator control station is usually larger or smaller than the actual value.

3. Poor contact of the wiring terminals inside the junction box. Due to the hardness of the compensating wires and wear-resistant thermocouple wires, it is difficult to tighten the wiring during on-site maintenance. Sometimes, the wires are tightened at the beginning but become loose again after a period of time due to deformation. This type of fault is reflected in the temperature display value on the operator control station being out of range with no display value.

4. Compensate for thermocouple faults. This type of fault manifests as a slow increase or decrease in temperature display value after the wear-resistant thermocouple is connected.

5. The temperature input signal malfunctioned after passing through the isolator, and the abnormal temperature value signal reflected on the operator control station. Normal after replacing the isolator. The above are common problems encountered during maintenance, but when searching for these faults, it is recommended to first use a multimeter to measure the input voltage value on the I/O terminal cabinet of the DCS. This can quickly determine whether it is a problem with the local measurement terminal or the DCS part. For multi-point input, it can also be compared with signals from several other thermocouples. If the resistance value cannot be determined by further measuring the wire, usually the wear-resistant thermocouple value is around 100 Ω.

6. Poor grounding inside the DCS cabinet of the signal shielding system. Such faults can easily cause charge accumulation on the signal line, leading to signal drift or jitter. Due to the difficulty in identifying the fault point of this issue, the usual solution is to disconnect the signal line and perform a grounding point treatment on it.