Decision Tree: Unstable O₂ Reading
Symptom: reading fluctuates, noisy, unstable trend.
Rule: Do not calibrate until reading stabilizes.
Isolation steps
1) Check sample flow and pressure stability. Confirm there is no regulator hunting.
2) Check for leaks / air ingress on sample lines, fittings, and manifold. Tighten and re-check.
3) Check moisture/condensation:
- Drain traps/knockout pots if fitted
- Confirm heat tracing is on (if required)
- Replace wet filters
4) Verify calibration gas stability (if on cal): correct cylinder, stable regulator, no leaks in cal manifold.
5) Electrical check:
- Check sensor wiring terminals for looseness
- Verify proper grounding/earthing
- Inspect for water ingress in junction boxes
6) If still unstable after sample & wiring checks:
- Suspect sensor aging or contamination
- Check sensor temperature stability (if heated)
Field tip: If the reading becomes stable on calibration gas but unstable on process sample, the issue is likely in the sample conditioning (process moisture/pressure swings).