Industrial Maintenance Technician how-to
How to Troubleshoot a PLC Input That Isn’t Working
Many “PLC problems” are really field device or wiring problems.
Many “PLC problems” are really field device or wiring problems. In short: identify; activate; if, then complete the remaining steps below.
Step by step
Identify the input address from the prints and check the PLC’s input indicator light.
Activate the sensor or switch and watch whether the indicator changes.
If no change, check the field device: power, alignment, target distance and its own indicator.
Measure voltage at the input terminal with a meter.
Check wiring, connectors and fuses between the device and the PLC.
Replace the faulty component and verify the input in the PLC software.
Document the fix in the CMMS.
Safety reminders for industrial maintenance technicians
- Always lock out and verify zero energy before reaching into machinery
- Keep guards in place and replace them after maintenance
- Use NFPA 70E practices when working on electrical equipment
- Wear hearing and eye protection on the plant floor
Key terms
Preventive maintenance (PM) · Predictive maintenance · PLC · Ladder logic · VFD · Hydraulics: see the full industrial maintenance technician glossary.