Cylinder Reaches the End but the PLC Still Waits? Check the Magnet and Switch Position
A cylinder can complete its stroke while its position sensor never provides the expected signal. The sensor may be misplaced, incompatible, or responding outside the required position window. Separate actual mechanism position from the electrical indication before changing sequence timeouts.
Original endpoint-detection checklist; exact sensing requirements come from the installed product manuals.
What is happening?
Cylinder-mounted magnetic sensing depends on the actuator and sensor combination, installation position, and switching characteristics. A signal seen somewhere during travel is not equivalent to reliable confirmation at the intended endpoint. Mechanical stops and the sensor's detection zone must be considered together.
Check these five things
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Confirm the cylinder and sensor part numbers and their documented compatibility.
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Observe physical end position through the approved procedure and compare it with the sensor's own indication.
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Check mounting position, retention, and the intended sensing window using manufacturer guidance.
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Trace the sensor output through the wiring and PLC mapping if its local indication is correct.
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Test repeatability across normal travel and operating conditions without bypassing sequence conditions.
Worked example
A sensor switches briefly just before the cylinder reaches its mechanical stop, then turns off at the final position. A slow online display can make the event confusing. The problem may be the installed detection window rather than a failed PLC input.
Quick diagnostic reference
| Evidence | Next check |
|---|---|
| No local sensor indication | Compatibility and position |
| Local indication correct | Electrical path and mapping |
| Brief pulse only | Detection window and actual endpoint |
The mistake to avoid
Increasing a timeout cannot make an absent position signal valid. Establish why the expected confirmation is missing.
How to verify the fix
Confirm stable endpoint indication and correct clearing when the actuator leaves that position, following the machine's commissioning requirements.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Festo support portal: locate the installed actuator and sensor documentation. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.