Industrial Sensor Selection & Replacement Guide

How to pick the right replacement sensor — NPN vs PNP, NO vs NC, shielded vs unshielded — and swap it without guessing.

Quick diagnosis table

SymptomLikely causeAction
Sensor never switchesWiring type mismatch (NPN/PNP) or no supplyVerify output type against old sensor
Sensor always onSensing distance too short / target wrongCheck target material and gap
Intermittent switchingLoose M12 connector or cable breakWiggle test, replace cable
False triggers from nearby metalUnshielded sensor near metal mountingSwitch to shielded or flush type
LED flickers on power-upSupply voltage drop or load shortCheck 24V rail and load current

Step-by-step procedure

  1. Read the old sensor's marking: sensing type (inductive/capacitive/photoelectric), supply, output (NPN/PNP/relay), NO/NC, and rated sensing distance.
  2. Measure the actual sensing gap with the real target — a 2 mm unshielded sensor will not do a 5 mm job.
  3. Match the output type first: replacing an NPN sensor with a PNP unit (or vice versa) is the most common wrong-order mistake.
  4. Check the mounting: flush (shielded) vs non-flush (unshielded) determines how close metal can sit around the face.
  5. For photoelectric types, confirm the mode (through-beam, retro-reflective, diffuse) — they are not interchangeable even at the same range.
  6. Wire, power up and verify switching with the actual target at production speed, then cable-tie and label.

Replacement parts & selection notes

We supply replacement sensors across proximity, photoelectric, pressure, temperature and encoder feedback types, in PNP/NPN and NO/NC variants. Send a photo of the old sensor's label and we match it exactly — including M12 cordsets and mounting brackets.

Frequently asked questions

Can I use a longer-range sensor as a replacement?

Yes, as long as the output type, mounting and response frequency match — a longer range only reduces sensitivity to target variation.

NPN or PNP — how do I tell from the wiring?

NPN switches the negative side (signal sinks to 0V); PNP switches the positive (source +24V). If unsure, send the old sensor photo and PLC input card model.

Do you supply the M12 cable with the sensor?

Yes — 3/4/5-pin cordsets in standard lengths, matched to the sensor's pinout.

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