Portable (multi-gas) detectors used in confined spaces and maintenance work directly protect workers. Accuracy management is critical, yet a common misconception on site is that a bump test is enough. This guide from a KOLAS-accredited laboratory (no. KC23-416) walks through how portable detector calibration actually works and how it differs from a bump test.
Bump test ≠ calibration
| Bump test | Calibration | |
|---|---|---|
| Purpose | Confirm the sensor responds and the alarm sounds | Adjust readings to match standard gas concentration |
| Guarantees accuracy | No | Yes |
| When | Routine, before each use | Periodic (commonly 12 months) |
| Certificate | None | KOLAS-accredited certificate available |
They complement rather than replace each other: bump test routinely to confirm function, calibrate periodically to restore accuracy.
How calibration proceeds
- 1. Pre-check — housing, sensor condition, battery, and pump (for pumped units) are inspected. An expired sensor cannot be fixed by calibration and must be replaced first.
- 2. Zero calibration — in clean air (or zero gas), the baseline is set so the reading shows 0 (20.9% for oxygen).
- 3. Span calibration — certified standard gas of known concentration is applied and the sensitivity adjusted until the reading matches. This is the core of calibration.
- 4. Verification and records — before/after readings and errors are recorded, and alarm setpoints verified.
- 5. Certificate — a KOLAS-accredited certificate is issued. See the certificate guide for what it contains.
Courier calibration suits portables
Portables are small enough that courier calibration is usually the most convenient — inbound and on-site are also available. Check the calibration process, and send us the model, quantity, and target gas for a quick schedule and quote.
