Eddy current displacement sensors are commonly used measuring instruments that can accurately measure the static and dynamic relative displacement changes between the measured object (which must be a metal conductor) and the probe end face. They have advantages such as flexible use, stable performance, high reliability, and easy maintenance.
Accurate measurement of vibration and displacement is crucial for stable operation. Vibration and displacement probes are usually installed in pairs. If one of them malfunctions, and the temperature and other relevant process parameters at that point are normal, the alarm can be considered false. Based on years of experience, eddy current sensor design engineers have identified several main reasons that can cause false alarms.
Probe installation quality factors
False alarms caused by probe installation quality issues include loose or extended probe locking nuts, loose or poor contact cable joints, and stripped or loose preamplifier connectors.
Troubleshooting: When installing the probe, use appropriate tools to tighten the nuts firmly. Loose nuts are unlikely to occur during operation. However, due to repeated disassembly and assembly and long-term operation of the system, loose intermediate adapters or poor contact may occur during operation. Therefore, it is necessary to clean the oil and impurities at the joints during each maintenance and to ensure proper insulation and sealing at the joints. To ensure that the intermediate joints are tightened, you can tighten them by hand and then tighten the retaining ring with needle-nose pliers.
False alarms caused by faults in the measurement circuit
Common causes of false alarms due to faults in the measurement circuit include loose or poor contact of the preamplifier terminals, probe extension, cable insulation damage, and grounding of the circuit shield.
Troubleshooting methods: These types of faults are not easy to diagnose, and thorough inspection is not convenient during production operation. If a problem is found, the troubleshooting methods are as follows: For false alarms caused by loose terminals or poor contact, the problem can be addressed after the interlock at that point is released. For cable insulation damage, oil-resistant sealing tape or heat shrink tubing can be wrapped around the damaged area. If the line shielding wire is grounded, the wiring needs to be reconnected and anti-grounding measures should be taken. The crimp terminals at the preamplifier are prone to damage after repeated crimping and cannot be crimped tightly. Due to the overall structure of the preamplifier, it is difficult to repair damaged terminals, and a new preamplifier must be replaced, which results in a lot of waste. It is recommended to add a terminal block between the preamplifier and the cable. In this way, the crimp terminals at the preamplifier only need to be connected once, and subsequent line inspections can be performed at the newly added terminal block.
False alarms caused by probe malfunction
Such faults cannot be handled during unit operation and require shutdown. During equipment handling and disassembly, the probe's measuring coil may be damaged due to collisions and wear. Therefore, inspection and calibration must be performed before each installation. First, a visual inspection is performed. Without visual inspection, use a multimeter to measure its DC impedance. If there are obvious defects and the impedance is within the specified range, the probe is intact. If there are obvious defects, such as wear at the end or significant cable sheath damage, after repairing the damage, in addition to measuring the impedance, a dedicated sensor standard calibration is required. Only after the calibration result is satisfactory can the probe be used. Regardless of the fault type, during unit operation, on-site inspections can only include the following: With the interlocks released, check if the wiring is normal, if the preamplifier terminals are loose, and if the preamplifier power supply voltage is normal. If the probe's intermediate adapter is inside the unit casing or external protective tube, check if the intermediate adapter is loose and if the insulation is good. If further inspection is required, shutdown is necessary.
