Why these terms matter
Many site disputes happen because people mix up terms like drift, validity, response time, and wet/dry basis. This module gives you practical meanings — not textbook definitions.
Core Terms (Technician Meaning)
Zero
Check of baseline reading using zero gas (e.g., nitrogen or zero air). If zero is unstable, suspect leaks, flow issues, or contamination.
Span
Check of sensitivity using a known concentration. Span issues often indicate restriction, regulator instability, or sensor aging.
Drift
Change in analyzer reading over a defined time. Drift usually points to sample system problems or sensor contamination.
Validity / Data Flags
Periods when data is not reportable (calibration, faults, warm-up). If DAHS isn’t flagging correctly, you will have compliance headaches.
Response Time
Time for analyzer to reach stable reading after a change. Slow response is commonly caused by low flow, long lines, plugging, or condensation.
Linearity
Analyzer accuracy across multiple points (low-mid-high). If linearity fails, suspect wrong ranges, bad calibration gas, or sensor degradation.
Range / Span Factor
Measurement window (e.g., 0–200 ppm). Wrong range causes poor resolution and unstable control.
Wet/Dry Basis
Reporting basis depending on moisture correction method. Misunderstanding this causes “wrong value” arguments during audits.
Field quick-check checklist
- Is the analyzer warmed up and stable?
- Are you on the correct range?
- Is the calibration gas correct and in-date?
- Is sample flow stable (no restriction)?
- Any leaks in sample/calibration manifolds?
- Is DAHS flagging calibration and faults properly?