Limit switches & sensors
Proximity, photo-eyes, and position switching.
Limit switch or proximity sensor not being detected
A limit switch or proximity/photo sensor isn't registering — the machine doesn't stop at position, the input never makes, or the sensor LED looks wrong for the target's position.
Proximity sensor permanently on (always made)
A proximity sensor reads 'detected' all the time — its output stays on even with no target present, so the controller always sees the input made.
Sensor intermittent / drops out randomly
A sensor works most of the time but drops out or false-triggers intermittently, causing random stops, miscounts, or sequence faults that are hard to pin down.
Photoelectric sensor not detecting
A photo-eye (through-beam, retro-reflective, or diffuse) isn't detecting reliably — it misses the target, or the output doesn't change when something blocks/enters the beam.
Limit switch stuck made (won't release)
A mechanical limit switch stays operated even after the actuator leaves it — the input stays made, so the machine thinks it's still at that limit.
Analogue sensor (4-20mA / 0-10V) reading wrong
An analogue sensor (pressure, level, temperature) gives a wrong or fixed reading — stuck at zero, pinned at full scale, or simply not matching reality.
Encoder feedback fault (position/speed wrong)
Position or speed feedback from an encoder is wrong — counts drift, position is lost, or a drive faults on encoder loss, so motion control misbehaves.
Safety light curtain keeps tripping the machine
A safety light curtain is stopping or preventing the machine from running — it shows blocked/faulted even when the access area looks clear.
Float / level switch not operating
A float or level switch isn't controlling correctly — a pump won't start/stop on level, a tank overfills or runs dry, because the level switch isn't changing state.
Proximity sensor triggering at the wrong distance
A proximity sensor detects, but at the wrong point — too early, too late, or inconsistently — so positioning or counting is off even though the sensor 'works'.