What you'll learn
**Reported symptom:** The valve local display is at 50%, but PLC feedback is consistently 7.5% high across the range.
Lab time: ~15 minutes.
Lesson briefing
Analog Valve Feedback Drift
Reported symptom: The valve local display is at 50%, but PLC feedback is consistently 7.5% high across the range.
The circuit was commissioned from a known-good drawing. Treat every terminal as suspect, but test from source to load instead of guessing. Use voltage mode on an energised control circuit and continuity only after the simulated circuit is isolated.
Your task
Compare the loop signal at the valve, marshalling terminals and PLC input, then separate wiring loss from calibration offset.
Choose the fault category only when the measurements support it.
Hints
A fixed offset across several test points suggests zero/calibration drift rather than changing wire resistance.
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This lesson uses 7 placed components on the lab canvas. Components are vendor-neutral (no proprietary trademarks); the wiring rules apply to any equivalent industrial part.
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