Analysis of the causes of working faults in wear-resistant thermocouples

Wear resistant thermocouple is a special material thermocouple classification. It is a wear-resistant protective tube mainly composed of plasma spray painting technology, high chromium cast iron, and high-temperature alloy materials. It can be customized for different temperature environments and is suitable for use in circulating fluidized beds, boiling furnaces, and cement rotary kiln tail chambers. There are also many faults in the use of wear-resistant thermocouples, and attention should be paid to some details. Troubleshooting mainly includes the following precautions:.

1. The insulation layer of the compensating wire of the wear-resistant thermocouple is worn out, forming a signal circuit grounding. This is mainly due to the fact that the compensating wire is relatively hard and not placed flat inside the junction box. When dealing with the problem, repeatedly twisting the junction box cover would cause it to come into contact with the compensating wire and wear it out. This type of problem 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 primarily a problem presented during infrastructure construction, caused by the carelessness of the personnel responsible for wiring, which is due to human factors. When the compensation wire of the thermocouple is reversed, the display on the operator control station is generally larger or smaller than the actual value (depending on the channel measurement circuit).

3. Poor contact of the wiring terminals inside the junction box. Due to the hardness of the compensation wire and thermocouple wire, it is difficult to tighten the wiring during on-site maintenance. Sometimes, the wire is tightened at the beginning but becomes loose again after a period of time due to the deformation of the wire. This type of problem is reflected in the temperature indication on the operator control station being either no display or the displayed value exceeding the range.

4. Compensation resistor malfunction. This type of problem manifests as a slow increase or decrease in temperature readings after the thermocouple is connected.

5. The failure rate of measuring thermocouples in the tail flue of boilers is relatively high. When the thermocouple was shut down for maintenance, it was found that the head of the thermocouple, including the protective sleeve, was severely worn due to the erosion of smoke. The protective sleeve was made of wear-resistant steel material to eliminate this hidden danger.

6. The temperature input signal malfunctioned after passing through the isolator, reflected in the abnormal temperature value signal on the operator control station. Normal after replacing the isolator. The above are common problems encountered during maintenance, but when searching for these issues, 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 distinguish 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 measuring the line again, the resistance value of a wear-resistant thermocouple is generally around 100 Ω.

7. Poor grounding inside the DCS cabinet of the signal shielding system. This type of problem is prone to the accumulation of charges on the signal line, causing signal drift or jitter. Because the problem is difficult to identify, the general solution is to disconnect the signal line and perform ground discharge treatment on it.