One of the three has no mandatory performance certification at all. Another certifies the complete system rather than the instrument, and lists the parts it contains.
Which one you are in decides whether a module change is a purchasing decision or a re-certification.
The three regimes
| A. Safety detection | B. Emissions compliance | C. Process analysis and control | |
|---|---|---|---|
| Applies to | Flammable gas leak detection in hazardous areas | Stationary source emissions monitoring | Process optimisation and quality control |
| Mandatory standards | EN/IEC/UL 60079-29-1 (point type), 60079-29-4 (open path), 60079-0 (general) | EN 15267 series (QAL1), EN 14181 | None |
| What gets certified | The equipment | The complete measurement system | Defined by the owner’s or EPC’s specification |
| Output unit | %LEL or ppm; for open path, LFL·m | mg/m³ | Process units |
The third column is not an omission. In process analysis there is no mandatory performance certification, which means the competitive rules there are completely different: no certificate to hold, no certificate to lose, and specifications set by whoever writes the project document.
The exclusion clause most module datasheets do not mention
EN/IEC 60079-29-1 states what it does not apply to. The list includes:
- external sampling systems
- laboratory or research instruments
- equipment used only for process control
- open-path (line-of-sight) area monitors
Read that against how TDLAS is actually deployed. Its two most common forms — in-situ cross-stack process analysis, and open-path area monitoring — neither falls within 60079-29-1’s scope.
The consequences are not small:
- If your target application is safety alarm with an open path, the applicable standard is 60079-29-4, not 29-1.
- If your instrument is for process control only, no mandatory performance certification applies to it at all.
- A supplier telling you their module “meets 60079-29-1” has told you something that may not apply to the form you are building.
This is a scope question, and it comes before any performance question.
Optical path length decides which track you are on
60079-29-4 covers open-path equipment with path lengths from roughly one metre to several kilometres. Its output is the integrated concentration along the path, expressed as LFL·m — not a point concentration. Only where the concentration can be confirmed uniform along the path can an actual concentration be inferred, and the standard’s own example of that case is a very short path, under about 100 mm — which falls back into 60079-29-1’s scope.
So the optical path length simultaneously fixes four things:
- Sensitivity — longer path, more absorption
- Which standard applies — 29-1 or 29-4
- What unit you can report — ppm/%LEL, or LFL·m
- Whether you can give a point concentration at all
Path length is not a design preference. It is a regulatory decision made in optics. If you are specifying a module and the path length is still open, that decision has not been made yet — and it is upstream of everything on the datasheet.
QAL1 certifies the system, and lists what is in it
In the emissions compliance regime the certification object is not the analyser.
A QAL1 assessment covers the analyser together with the sample transport and pre-treatment system — sampling probe, heated lines, conditioning. It is an assessment of a complete measurement system, and the components that constitute the certified system are listed in the certificate.
What we think follows — and we are asking rather than asserting
If the certificate lists the constituent components, then replacing the analysis module inside a certified system very likely affects the validity of that certificate.
This is an inference, not an established fact
We derived it from the certification scope described above. We have not obtained a certification body’s written rule on component change and certificate maintenance, and we are not going to present a derivation as though it were a documented rule.
If it holds, the consequence for anyone selling modules into compliance applications is significant:
- The replacement channel in already-certified systems is effectively closed.
- The entry point is only when a manufacturer specifies a new system.
That changes when a module can be sold, not just what gets sold — and it is the single thing we most want confirmed or refuted.
If you know the answer for your scheme, we would like to hear it. It is the kind of rule that lives inside certification bodies and equipment manufacturers, and does not appear in public documents. We looked.
Three questions to answer before you compare modules
- Which regime is my instrument in? Safety detection, emissions compliance, or process control. If the answer is process control, there is no mandatory performance certification and your specification is whatever your customer’s project document says.
- What does my optical path put me under? Under about 100 mm and you are in point-detection territory with a point concentration output. A metre or more and you are in open-path territory with an integrated output in LFL·m. This is settled in optics, not in software.
- What does my certificate list? If your instrument is certified as a system, find out what the certificate names, and ask the certification body what a component change triggers. That answer sets how locked in you are to your current supplier — including to us.
Where this leaves us
We build measurement modules that go inside someone else’s instrument. Under the regimes above, that means:
We do not hold a performance certificate for your application, and in regime C there is none to hold. What we supply is the module and the documentation your assessment needs — test conditions, component traceability, integration documentation.
When we are relevant, and when we are not
In regime A or B, if your instrument is already certified, the question in the inference section applies to us as much as to any other supplier. If a module change triggers re-assessment in your scheme, then we are relevant at your next new design and not before. We would rather say that than take you through a qualification that ends there.
In regime C there is no certification gate, and the constraint on module choice is your own specification and your customer’s project document.
Telling you which of these you are in is not something we can do from here. It is the first question on the project qualification form for that reason.