What changes when concentration rises
| Measurement region | What matters | Why one full-scale claim is not enough |
|---|---|---|
| Low end | Absolute error, baseline stability, path length and signal-to-noise. | A path that is too short may lose low-end sensitivity. |
| High end | Optical headroom, detector response, gas-cell condition and signal linearity. | A path long enough for low concentration can saturate at high concentration. |
| Decision threshold | Error band at the actual threshold, under the relevant rule set. | A single percentage-of-full-scale number can hide an unacceptable band at the decision point. |
Why Line B uses a target range, not a promise
Line B is being developed around a 0–100 %vol CH₄ target range for the drainage scenario. The current target model separates a low segment and a high segment so the error language can match the decision use. Final accuracy and response remain target values until the stated gas, pressure, temperature and flow conditions are tested.
At high concentration, the application question is not just “can the display show 100?” It is whether the measurement chain behaves predictably at the pressure, flow and interlock thresholds that matter to the host system.
Read the range with the test conditions
- Gas composition and background gas
- Absolute pressure and pressure compensation method
- Temperature and warm-up state
- Flow path, flow rate and gas arrival
- Optical path, gas cell and configuration
- Accuracy segment, response definition and evidence status
A range is not a capability claim until the conditions that make it valid are stated and supported.
FAQ
Questions engineers ask next
Can software alone extend a module to 0–100 %vol?
Do not assume so. Optical path, gas cell, detector signal and calibration conditions may all need to change.
Why publish accuracy in segments?
Absolute error is meaningful at the low end, while percentage of reading is often more meaningful at the high end. One full-scale percentage can hide an unrealistic requirement at one end of the range.
Does a 0–100 %vol target mean the final accuracy is certified?
No. It is a target application range. Final accuracy, pressure compensation and response require stated conditions and project or bench evidence.
Why does the gas path belong in the range discussion?
Gas arrival, cell exchange, pressure and optical path length affect the signal and response. The range cannot be separated from how gas reaches the measurement path.