Gas Analyzer Calibration

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Practical Procedure · Calibration

Gas Analyzer Calibration — Zero and Span, Zirconia / NDIR

Applies to: Zirconia oxygen analyzers, NDIR (CO/CO2/SO2 etc.) analyzers  |  Equipment needed: Zero gas cylinder, span gas cylinder (certified concentration), flow regulator

Zero and Span — See the Flow

Tap a tab to switch the diagram, then tap "Show Correction" to see the reading before and after calibration.

Zero Gas Cylinder Cert. 0.0% Analyzer Zero adjust 1.8% 0.0% reading vs 0.0% Output Signal to PLC/DCS 4–20 mA / digital
Span Gas Cylinder Cert. 20.9% Analyzer Span adjust 19.4% 20.9% reading vs 20.9% Output Signal to PLC/DCS 4–20 mA / digital
Zero gas establishes the analyzer's low-end reference — usually nitrogen or a certified zero-concentration gas.
Span gas establishes the high-end reference near the top of the operating range — always calibrated after zero, never before.

Step 1 — Zero Gas Calibration

  • Isolate the analyzer from the process sample and connect the zero gas cylinder (typically nitrogen, or a certified low/zero-concentration gas for the target component).
  • Flow zero gas at the specified rate and allow the reading to stabilize fully — rushing this step is one of the most common sources of calibration error.
  • Adjust the zero setting until the analyzer reads the certified zero gas value correctly.

Step 2 — Span Gas Calibration

  • Switch to the span gas cylinder — a certified concentration near the top of your normal operating range.
  • Flow span gas at the specified rate and allow the reading to stabilize.
  • Adjust the span setting until the analyzer reads the certified span gas concentration correctly.
  • Always calibrate zero before span — adjusting span first and then correcting zero will throw the span reading off again.

Calibration Frequency and Drift Patterns

  • Zirconia (O2) cells — cell output gradually weakens with age and high-temperature exposure. Watch for slow, gradual drift over weeks/months rather than sudden jumps; a sudden jump usually points to a sample flow or fitting problem rather than the cell itself.
  • NDIR analyzers — optical bench components (source, detector, filters) can drift with dust contamination or optical window fouling. Watch for span drift specifically after periods of high dust loading in the sample gas.
  • Set calibration frequency based on your process criticality and observed drift rate — a cell/bench trending steadily in one direction between calibrations tells you it's time to shorten the interval, not just note the deviation and move on.

Common Mistakes to Avoid

  • Not allowing full stabilization time at each gas step before adjusting.
  • Calibrating span before zero.
  • Using expired or uncertified calibration gas — the calibration is only as good as the gas concentration you're trusting.
  • Assuming every reading drift is a cell/bench problem without first checking sample flow, fittings, and filters (a flow restriction can mimic a failing cell — see the zirconia fault case study on this blog).
Intermediate/Advanced Electrical Theory — Interactive Animated Course (Part 2)

This is a general field procedure — specifics vary by analyzer brand and plant calibration standards. Adjust to your own SOP where needed.

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