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.
Safety first
A stuck-on sensor can make a machine think it's in a position it isn't. Confirm actual position before moving anything based on the input.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Target/metal too close or fixed metal in range
Most likelyFixed metal within the sensing range, or the gap set too small, keeps an inductive prox permanently triggered.
- 2
Sensor output short / failed on
#2The sensor's output transistor has failed in the conducting state, holding the signal on.
- 3
Wiring short to the active line
#3A cable short or pinched wire holds the input line at the active level regardless of the sensor.
- 4
Wrong sensor type for the application
Least likelyA normally-closed (NC) sensor used where NO logic is expected reads as always-on.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeRemove all targets and check the sensor's indicator LED and output state.
Output turns off with no target in range.
Sensor releases — your 'always on' was a present target; check positioning.
Stays on with nothing present — check for fixed metal, then the sensor/wiring.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Prox always on
→ step 2 - 2decision
Does the output turn off with no target present?
Yes→ step 3No→ step 4 - 3result
It was a present target — check positioning/gap.
- 4decision
Is there fixed metal in range or the gap too small?
Yes→ step 5No→ step 6 - 5result
Reposition / adjust the gap.
- 6decision
Does the input clear when the sensor is disconnected?
Yes→ step 7No→ step 8 - 7result
Sensor failed on — replace (confirm NO/NC).
- 8result
Wiring short to the active line — find and repair.
Common mistakes apprentices make
- Not realising fixed nearby metal keeps an inductive prox triggered.
- Confusing an NC sensor's 'always on at rest' behaviour with a fault.
- Blaming the sensor when a pinched cable shorts the line.
- Setting the sensing gap too small.
When to stop & escalate
If a stuck input affects a safety or positioning interlock, treat position confirmation as critical before any movement. Replace a failed sensor rather than working around it.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
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.
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.
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.
Learn the theory
How the gear and circuits behind this fault actually work.