I. Observing Abnormal Operational Phenomena
1. If the belt slips at low speed, breaks, or overspeeds, and the protection device does not trigger a stop or alarm, it indicates that the sensor is not responding correctly to speed changes.
2. Press the self-test button on the sensor housing. If the fault indicator light does not illuminate, it indicates that the alarm circuit or indicating element has failed.
3. Frequent false alarms or unexplained malfunctions in humid or dusty environments may be due to sealing failure, internal moisture, or magnet contamination.
II. Electrical Parameter Testing
1. Power Supply Check: After powering on, use a multimeter to measure the voltage at the sensor's power supply terminals (E and O) to confirm that it is within the DC 12V~24V range. Abnormal voltage may cause unstable signal output or no output at all.
2. Resistance Measurement (Power Off Operation): After disconnecting the power supply, use a multimeter to measure the resistance between the two pins of the sensor. The normal value should be between 0.7 and 1.2kΩ (e.g., GS4(A), GSC6 type). If the resistance is infinite (open circuit) or close to zero (short circuit), the internal coil or magnetic sensing element is damaged.
3. Signal Output Test
Use an oscilloscope connected to the signal output terminal (V), manually rotate the sensor drum, and observe whether the output waveform is a stable, regular pulse signal. If the waveform is messy, missing, or has abnormal amplitude, it indicates that the sensing element has failed.
Connect an ammeter in series at the constant current output terminal to check whether the output is stable at 5±0.5mA. If it deviates from this range, check whether the internal potentiometer W2 has drifted or the circuit is aging.
III. Functional Simulation and Verification
1. Manually rotate the sensor drum and simultaneously observe whether the matching protection host (such as ZJZ-SZ(A)) receives the corresponding speed signal. If the host does not respond and the circuit is normal, the sensor itself is faulty.
2. Use the substitution method: Replace with a known working sensor of the same model. If the system returns to normal operation, the original sensor is confirmed to be faulty.
IV. System Diagnosis and Fault Code Reading
1. Read fault codes through the diagnostic interface of the mining protection device (such as ZJZ-SZ(A)) or the monitoring system. Common codes include "Fault Code 11," which clearly indicates an abnormal speed sensor signal or communication interruption.
2. Some systems may record P0500 series fault codes (derived from automotive standard extensions), indicating sensor signal loss or instability. Their applicability needs to be confirmed in conjunction with the equipment manual.
V. Environmental and Mechanical Inspection
1. Check whether the sensor roller is in close contact with the underside of the belt, and whether there is wear, dust accumulation, or foreign object jamming that could affect magnetic induction accuracy.
2. Check whether the mounting bracket is loose, and whether the cable has internal wire breaks or joint oxidation due to long-term vibration.
3. Confirm that the wiring port is properly sealed, with no methane or coal dust seeping in to prevent intrinsic safety failure.
VI. Safety Precautions
1. All tests must be performed with the power off. Only non-contact testing is permitted when power is on.
2. Unauthorized replacement of intrinsically safe circuit components, modification of parameters, or connection of uncertified equipment is strictly prohibited. Violation of this rule will result in the loss of explosion-proof certification and may lead to an explosion risk.
3. Regular calibration and preventative replacement are crucial for ensuring long-term reliable operation, especially in mine environments where continuous operation has exceeded 5 years.
