Contrinex Photoelectric Sensor — No Detection

Contrinex · beginner · 15 min

A Contrinex photoelectric sensor that misses the target or won't switch its output is usually a teach/alignment/mode problem, not a failed sensor. Learn to check the sensing mode, re-teach the setpoint, confirm light-on/dark-on, and verify the PNP output.

ℹ️ A Contrinex photoelectric sensor detects by teach-in. If it isn't switching, first ask which mode it's in — diffuse, background-suppression, or polarized retroreflective — because each fails differently. Then re-teach, check light-on/dark-on, and confirm the PNP output wiring.

Know the sensing mode

Contrinex photoelectric sensors work in different styles, and the fix for "no detection" depends on which one you have:

• Diffuse — detects light bounced back off the target itself. Sensitive to target colour/finish and distance.
• Diffuse with background suppression (BGS) — detects within a set distance and ignores anything beyond it. Great for ignoring a busy background, but the setpoint distance must be right.
• Polarized retroreflective — the beam goes to a reflector and back; the target breaks the beam. Needs the reflector aligned and clean.

Sensing distances run up to 7 m depending on model. Identify the mode before troubleshooting — a BGS sensor "not seeing" a near target is a setpoint issue, while a retroreflective one is usually reflector alignment.

Re-teach the setpoint

Contrinex smart photoelectric sensors use a teach-in function (and can teach up to three separate outputs), letting the sensor recognise or ignore even small variations. If detection is marginal or wrong:

1. Present the actual target (and, for BGS, the actual background) and re-teach the setpoint.
2. Start around medium sensitivity and adjust based on the target's properties and the environment.
3. For fussy targets (shiny, dark, translucent), teach against the real part rather than a stand-in.

Check light-on / dark-on and the output

• Light-on vs dark-on: the output logic is selectable. If the sensor detects correctly but the PLC sees the opposite of what you expect, the light-on/dark-on setting is inverted — switch it.
• Output wiring: these sensors provide a PNP output plus a configurable discrete/IO-Link output. Confirm the PNP output is wired to a sinking PLC input, the load is within spec, and (if used) the second output/IO-Link is configured for what you expect.

Clean and align

Basic but common: clean the optical surfaces and do a periodic alignment check. A filmed lens or a nudged reflector mimics a dead sensor.

Step-by-step

1. Identify the mode (diffuse / BGS / retroreflective) — it dictates the likely cause.
2. Clean the lens (and reflector) and check alignment.
3. Re-teach the setpoint against the real target/background; start at medium sensitivity.
4. Check light-on/dark-on if the switching sense is inverted.
5. Verify the PNP output wiring and the second/IO-Link output configuration; test on real parts.

Never do this

Don't crank sensitivity to the maximum just to force a marginal diffuse detection — you'll pick up the background and get false triggers. Use background suppression or a retroreflective setup for a reliable, well-separated switching point.