⚠️ Disclaimer: These tasks are guidelines only. They do not include lockout/tagout (LOTO), energy isolation, or other safety requirements. Review and verify suitability for your specific equipment and application. Add all required safety procedures per your company's policies and regulatory requirements before use. You are responsible for the safe and appropriate execution of all maintenance activities.
Proximity sensors fail in ways that are easy to miss. The LED is on. The signal is present. And the machine is counting parts that aren't there, or missing parts that are. This checklist is for maintenance technicians and managers who want to catch those failures before the control system starts lying to them.
How to Use This Checklist
Record findings with specificity, not just a checkmark. "Sensor face clean" tells you nothing at the next PM. "Metal chip contamination on sensor face, cleaned — minor buildup typical for this location" gives you a trend. If you're seeing contamination every PM cycle at the same sensor, that's a mounting or guarding problem, not just a cleaning task. Note what you found, what you did, and whether the finding was the same as last time, better, or worse. That's the difference between a PM record and a maintenance record.
Field Checklist — Critical Tasks
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect sensor face (active surface) for dirt, oil, metal chips, or debris. Clean with a dry or slightly damp cloth. Do not use abrasive materials. | Every PM | MEC |
| Inspect sensor housing and cable entry for physical damage — cracks, dents, crushed housing, or bent conduit fittings. | Every PM | MEC |
| Inspect sensor cable or conduit for cuts, abrasion, pinching, or signs of heat damage. Follow cable run to the nearest junction box or control panel. | Every PM | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Verify sensor indicator LED is active and responding correctly when a target enters the detection zone. Confirm output state matches expected logic (normally open or normally closed). | Every PM | ALL |
| Verify sensor output is registering correctly at the PLC or controller input. Confirm correct I/O point, signal level, and no persistent faults or input errors in the controller. | Monthly | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Check sensor mounting bracket and hardware for looseness, corrosion, or shift in position. Re-tighten or re-align if needed. Confirm sensing gap is within specification. | Monthly | MEC |
| Verify sensor detection range using a target of the appropriate size and material. Confirm reliable switching at the intended distance. Adjust position if detection has shifted. | Quarterly | MEC |
Electrical Inspection
| Task | Freq | Type |
|---|---|---|
| Check all electrical connections at the sensor connector or junction — verify no corrosion, looseness, or damaged pins. Reseat connector and inspect seal condition. | Quarterly | ELE |
Reference Checklist — Full Task Library
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect sensor face (active surface) for contamination — dirt, oil, metal chips, weld spatter, or coating buildup. Clean with appropriate solvent-free method per sensor type. Heavy contamination may reduce effective sensing range and cause intermittent faults. | Every PM | MEC |
| Inspect sensor housing for physical damage — cracks, dents, impact marks, or bent threads. Check for signs of thermal stress or UV degradation on plastic housings (outdoor/high-temp installations). Replace damaged sensors before failure. | Every PM | MEC |
| Inspect sensor cable from the sensor body to the first termination point. Look for cuts, abrasion, kinking, pinching, or heat damage. Verify cable is properly supported and not subject to repeated flex or pull at the connector. | Every PM | MEC |
| Verify IP/NEMA rating integrity of the sensor installation — confirm all cable glands, conduit fittings, and connector seals are undamaged and fully seated. Replace cracked or compressed seals on sensors in wash-down, wet, or outdoor environments. | Quarterly | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Verify sensor indicator LED state during normal operation — confirm active output when target is in range and output release when target is removed. Confirm LED behavior matches the expected NC or NO wiring logic. | Every PM | ALL |
| Confirm sensor output is registering at the correct PLC or controller input point. Check for active faults, input bounce, or persistent error flags. Compare live I/O state against machine state to confirm logic is correct. | Every PM | ELE |
| Check sensor response time by observing output switching against a known-speed target or by manually cycling a target rapidly. Confirm no perceptible lag or missed pulses for the application's required cycle rate. | Semi-Annually | ELE |
| Perform a full functional verification — simulate target presence and absence through the full operating range of the machine cycle. Confirm all downstream logic, interlocks, and safety functions respond correctly to sensor state changes. | Annually | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Check sensor mounting bracket for looseness, vibration damage, or shift in position. Verify the bracket is not cracked or bent. Confirm sensing gap or angular position has not changed since last PM. | Monthly | MEC |
| Verify detection range using a target of the correct size and material for the application. Confirm the sensor switches reliably at the intended distance with acceptable hysteresis. Readjust mounting if detection point has drifted. | Monthly | MEC |
| Verify sensor part number and specifications against the current bill of materials or equipment record. Confirm sensor type (inductive, capacitive, photoelectric, etc.), sensing range, and output type match the application requirement. Flag any field substitutions. | Semi-Annually | ALL |
| Confirm spare sensor availability in the storeroom. Verify spare is the correct part number, is undamaged, and is ready for immediate swap-out. Replenish stock if below minimum quantity. | Annually | ALL |
Electrical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect all electrical connections at the sensor connector, inline junction, and at the panel terminal. Check for corrosion, pushed-back pins, moisture ingress, or loose ferrules. Reseat and reseal connectors as needed. | Quarterly | ELE |
| Measure and record supply voltage at the sensor (typically 10–30V DC or 12–24V DC). Verify voltage is within sensor nameplate specification. Low or fluctuating voltage can cause false outputs or reduced range. | Quarterly | ELE |
| Review sensor fault and diagnostic history in the PLC or SCADA system. Identify any recurring input errors, nuisance trips, or bouncing signals. Correlate findings to contamination, wear, or application drift. | Semi-Annually | ELE |
Failure Modes This Checklist Targets
Face Contamination Metal chips, oil film, weld spatter, or coating buildup on the active surface reduces the effective sensing range — the sensor stays on, looks healthy, and starts missing targets or detecting at inconsistent distances.
Cable and Connector Damage Industrial environments destroy cables through abrasion, repeated flex, and heat. A partially broken conductor causes intermittent signal loss that reads as a nuisance fault until the wire fails completely and the machine stops.
Mounting Shift and Sensing Gap Drift Vibration, impact, or thermal cycling moves the sensor. The sensing gap grows. Detection becomes unreliable at the exact moment machine speed or target geometry matters most.
Supply Voltage Degradation Low or fluctuating supply voltage reduces switching reliability and sensing range — often appearing as intermittent faults that are impossible to reproduce during troubleshooting because voltage recovers when the machine is idle.
Connector and Terminal Corrosion Moisture in wash-down environments or high-humidity locations works into connectors and panel terminals. Corrosion increases resistance. The sensor keeps sending a signal. The signal is wrong.
Logic Mismatch After Field Substitution Someone swaps a normally open sensor for normally closed, or installs a different sensing range without updating the documentation. The output type and range now conflict with the control logic. The machine runs, but the interlock doesn't work the way anyone thinks it does.
Related Checklists
- Sensors that detect by material properties rather than position: Inductive Sensor PM Checklist
- Sensors that detect non-metallic targets through capacitive field changes: Capacitive Sensor PM Checklist