Condensed from an OPSIS AB article by Bengt Löfstedt, first published 2018-03-15.
Technically there need be no difference at all between a gas analyser and a gas monitor. Semantically, analysis suggests a more scientific role, with higher accuracy and performance, while monitoring may suggest an indicative output where precision matters less. The words are nevertheless used interchangeably: multi-component gas analysers serve what is traditionally called ambient air quality monitoring and continuous emission monitoring, so calling them gas monitors is natural. Those applications do demand scientific-grade accuracy and precision, which is exactly why an analyser is needed — and an oxygen monitor also analyses the gas and reports oxygen concentration with high accuracy. At least one class of monitor is genuinely indicative: the sensors used for indoor climate and ventilation control. There it is enough to know whether the CO2 content is high or low and to drive a fan accordingly; such monitors are simple and inexpensive and entirely adequate for that purpose, but their performance does not support real ambient or emission monitoring. Either way, with gas instruments you generally get what you pay for.
In Chinese tender documents, technical agreements and day-to-day discussion the two words are treated as synonyms as well. What actually decides the selection is not the name but the performance figures and the applicable standard: a CEMS follows the HJ 75 and HJ 76 series, ambient monitoring follows GB 3095 and HJ 654, and their requirements for range, detection limit, calibration and data validity are difficult for an indicative sensor to meet. A useful test before specifying anything is to ask what the result will be used for. For trend observation or interlock control, such as driving ventilation, an indicative sensor is often sufficient; for emission reporting, compliance assessment or process optimisation, specify analyser-grade performance and check how calibration and traceability will be handled. Where volume and mass units both appear, calculate the conversion for the actual gas and conditions rather than applying a single factor.
What Is the Difference Between a Gas Analyser and a Gas Monitor — read the original at opsis.se ↗
Written by Bengt Löfstedt, OPSIS AB, first published 2018-03-15. The summary and the A.Johnson note above are our own text; the OPSIS article remains the authoritative version. Chinese reader? See the full Chinese article.
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