1、 Common faults and cause analysis

1. The indicator light is not on or there is no output signal

• Possible reasons：
  • Power issueUnstable power supply voltage, reversed polarity or open circuit of power line.
  • Switch damagedInternal circuit board burnout, oscillation circuit malfunction, or sensor head damage.
  • Connection issuesLoose wiring, oxidized plugs, or broken cables.
• Phenomenon description：
  • The switch indicator light is not on, and there is no input signal from the PLC or controller.
  • Measure that there is no voltage or current change at the output terminal.

2. Misconduct (output signal when there is no object)

• Possible reasons：
  • Environmental interferenceStrong electromagnetic fields (such as frequency converters, welding machines), high-frequency noise, or the influence of nearby large motors.
  • Testing material issuesThe test substance is non-metallic, the surface coating is too thick, or the size of the test substance is too small.
  • Installation issuesThe distance between the switch and the detection object is too close (exceeding the rated detection distance) or the installation surface vibrates.
• Phenomenon description：
  • When there is no metal object approaching, the switch output signal frequently jumps.
  • The failure rate increases in specific environments (such as near power lines).

3. No action (no output signal when there is an object)

• Possible reasons：
  • Insufficient detection distanceThe test substance has not entered the effective detection range or the detection distance has decreased (such as a decrease in sensitivity after long-term use).
  • The material of the object does not matchThe test substance is a non ferromagnetic material (such as aluminum, copper) and the switch has not been calibrated for this material.
  • internal faultThe oscillation circuit stops oscillating, the output stage is damaged, or the sensor head is contaminated.
• Phenomenon description：
  • The switch still does not respond when the metal object approaches within the rated distance.
  • When manually short circuiting the output terminal, the signal is normal and the controller fault is eliminated.

4. Unstable output signal (jitter)

• Possible reasons：
  • Uneven surface of the test substanceIf the test object is a rough metal sheet or a vibrating workpiece.
  • Environmental vibrationMechanical vibration causes frequent changes in the relative position between the detected object and the switch.
  • power fluctuationUnstable power supply voltage or excessive load current.
• Phenomenon description：
  • The output signal quickly switches between "0" and "1", causing the controller to misjudge.

5. The lifespan of the switch is shortened or frequently damaged

• Possible reasons：
  • Overloaded useLong term operation exceeding the rated current or voltage.
  • Poor environmentHigh temperature, high humidity, corrosive gases, or frequent mechanical impacts.
  • Improper installationThe switch axis is not perpendicular to the direction of motion of the detection object, resulting in unidirectional wear.
• Phenomenon description：
  • The switch will fail after several months of use, or the switch will be frequently replaced in the same position.

2、 Fault diagnosis and solutions

1. The indicator light is not on or there is no output signal

• Diagnostic Steps：
  1. Check if the power supply voltage is within the rated range (such as 24VDC ± 10%) and if the polarity is correct.
  2. Measure the voltage at the input power supply and output signal terminals with a multimeter.
  3. Check if the wiring is secure, if the plug is oxidized, and if the cable is broken.
  4. Replace the switch of the same model for testing to confirm if it is a malfunction of the switch itself.
• solution：
  • Correct the power wiring and replace damaged cables or plugs.
  • If the switch is damaged, contact the supplier for replacement or return to the factory for repair.

2. Inaction or non action

• Diagnostic Steps：
  1. Confirm whether the material, size, and surface condition of the test object meet the requirements.
  2. Adjust the distance between the switch and the detection object to within the rated range (e.g. 8mm rated distance, actual use 6-10mm).
  3. Check for strong electromagnetic interference sources (such as frequency converters, welding machines) around and attempt to isolate them.
  4. Use an oscilloscope or spectrum analyzer to detect the level of environmental noise.
• solution：
  • Replace switches suitable for non ferromagnetic materials (such as capacitor or inductor specific models).
  • Install a shielding cover or keep away from interference sources, and if necessary, use shielded cables and single ended grounding.
  • Re calibrate the detection distance or replace the switch with higher sensitivity.

3. Unstable output signal

• Diagnostic Steps：
  1. Observe whether the surface of the test object is flat, and whether there is vibration or shaking.
  2. Use a regulated power supply to supply power and check if the voltage fluctuation is within the allowable range (such as ≤ 5%).
  3. Install an RC filter circuit (such as a 0.1 μ F capacitor+1k Ω resistor) at the output end to suppress jitter.
• solution：
  • Improve the fixing method of the detection substance to reduce vibration.
  • Optimize power supply design, add filtering capacitors or use UPS.

4. Shortened lifespan of switches

• Diagnostic Steps：
  1. Check if the actual working current exceeds the rated value (e.g. NPN type maximum 300mA).
  2. Measure the ambient temperature and humidity to confirm if it exceeds the protection level (such as IP67).
  3. Check if the installation method causes unidirectional force (such as lateral impact).
• solution：
  • Choose switches with stronger load capacity or install relays for isolation.
  • Improve environmental conditions (such as installing protective covers and ventilation equipment).
  • Redesign the installation structure to ensure that the switch axis is perpendicular to the direction of movement of the detection object.

3、 Preventive measures and maintenance recommendations

1. regular cleaning：
   • Wipe the sensor head with a dust-free cloth every week to avoid the accumulation of oil stains and metal shavings that may affect sensitivity.
   • In dusty environments, install dust covers or choose sealed switches (such as IP69K).
2. environment optimization：
   • Stay away from strong electromagnetic interference sources (such as maintaining a distance of at least 1 meter), or use shielded cables.
   • Control the ambient temperature within the range of -25 ℃~+70 ℃ and humidity ≤ 85% RH (no condensation).
3. Correct installation：
   • Ensure that the switch axis is perpendicular to the direction of motion of the detection object, with a deviation of ≤± 5 °.
   • Use a dedicated installation bracket to fix and avoid position deviation caused by vibration.
4. Parameter Matching：
   • Select the appropriate type of switch (such as inductive or capacitive) based on the material of the test substance (such as iron, aluminum, copper).
   • Set the detection distance to 70%~80% of the rated value to leave room for environmental changes.
5. Spare Parts Management：
   • Reserve switches of the same model and commonly used accessories (such as cables and plugs) to shorten downtime due to malfunctions.
   • Record the usage time of the switch and regularly replace aging equipment (such as mandatory replacement every 2 years).