Fault Finding Guides · Free PDF
Fixed Gas Detector Fault Finding Guide
A one page guide to fixed gas detector problems: bump test failures, poisoning, drift, false alarms and output faults.
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A one page A4 guide to print for the workshop or keep on your phone in the field. The full content is also shown below.
Download PDF A4 · 52 KBBefore you start
- Permit, isolation and control room informed.
- Put the loop in manual or inhibit trips as authorised.
- Use certified test equipment in hazardous areas.
- Record as found readings before changing anything.
Quick checks
- Test gas correct and in date?
- Inhibit status known?
- Sensor within service life?
- Environment: dust, water, steam?
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Symptoms, causes and fixes
| Symptom | Likely causes | Checks and fixes |
|---|---|---|
| Fails bump test (low) | Poisoned catalytic sensor, blocked sinter, aged sensor | Clean or replace; calibrate |
| False alarms | Cross sensitive gases, humidity, steam, RF | Check process; relocate; filter |
| Negative or drifting zero | Calibrated in contaminated air, sensor ageing | Zero with zero gas; replace sensor |
| IR optics fault | Dirty windows, condensation | Clean optics; fit weather guard |
| No signal at DCS | Loop fault, inhibit left on | Check loop and inhibit status |
| Slow response | Blocked guard or sinter, long sampling line | Clean; check flow |
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Reminders
- Methane LEL 4.4 % vol (IEC 60079-20-1).
- Catalytic sensors need oxygen and can be poisoned by silicones.
- IR detectors do not detect hydrogen.
Related Tools, Procedures and Calculators
Frequently Asked Questions
Why does a catalytic detector read low?
Poisoning or inhibition by silicones, sulfur compounds or lead.
What is a bump test?
A quick gas exposure to prove response without adjustment.
Why do IR detectors give optics faults?
Dirt or condensation on the optical windows.
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