Integrating a gas detection module into your own product means committing to a supplier for the life of that product. The specification can be identical across three quotes and the outcomes can still differ by years of rework. These twelve questions are the ones that expose the difference, in roughly the order they start to matter.
On the sensing element
1. Who makes the sensing element, and is it the cell you will ship?
A module is an enclosure, a circuit and a cell. The cell decides the performance. Suppliers that buy from the same two or three cell manufacturers will produce similar readings, and the differentiation is in the electronics and the calibration.
Good answer: a named cell manufacturer and a part number, with an honest note about second sources.
Red flag: “our own cell” with no further detail. Almost nobody makes their own electrochemical cells.
2. What is the cell’s cross-sensitivity, and does the firmware correct for it?
A CO cell responds to hydrogen. An H2S cell responds to other sulphur compounds. Whether that matters depends on the application, and whether the supplier can tell you the figures decides whether you can answer your own customer.
On certification
3. Which approvals does the module itself hold, and whose name is on the certificate?
This is the question that separates a manufacturer from a trading company, and it is worth more than the other eleven combined.
A certificate for the finished instrument does not cover an unlisted module. A certificate in the supplier’s own name means they can support the marking through the life of the product. A certificate they are borrowing from a customer’s application may not be usable for yours.
4. If we obtain system certification, who handles the sample submission and the technical file?
Certification of a finished product requires the module supplier to provide documentation: construction drawings, bill of materials, component certificates, and often a factory inspection. Ask what they will provide and whether they have done it before for another customer, in a named market.
5. Which documents ship with each unit?
Minimum: datasheet, calibration certificate with the gas concentration and the instrument serial, and the declaration of conformity. For lithium battery products, UN38.3 test summary and the MSDS. If any of these is a PDF that cannot be produced on demand for an export shipment, the first order will be delayed at the port.
On the electronics and firmware
6. Is the firmware yours, and can the register map be changed for us?
A supplier with no firmware control cannot fix a bug without a third party, cannot add a customer-specific register, and cannot change a default. Ask who wrote the firmware and whether they are still available.
Good answer: “yes, here is the register map, we can add a customer block.”
Red flag: an inability to send a register map before a PO. If the document does not exist, the firmware is not theirs.
7. What is the failure mode on loss of communication?
Does the analogue output go to a defined state, hold the last value, or fall to zero? On a 4-20 mA channel, a fault current below 3.6 mA is a deliberate and useful convention. Holding the last good value is a silent failure that will be discovered during an incident.
8. What can be configured in the field, and what needs a factory tool?
A module whose alarm setpoints require a proprietary cable and a Windows application is a support burden for every one of your customers. A module with a documented register map is not.
On supply and commercials
9. What is the MOQ, the lead time at that MOQ, and the lead time at three times that MOQ?
Lead time at the minimum order is a number suppliers can hold. Lead time at volume is the number your production plan depends on. Ask both, and ask what the cell availability looks like separately, because the electronics and the cell are different supply chains and the cell is usually the constraint.
10. Who owns the tooling and the enclosure mould if we stop ordering?
If you paid for a mould, get it in writing that the tool belongs to you and can be transferred. If the supplier paid, understand that the enclosure is theirs and a second source will need a different one.
On the long term
11. What is the warranty, and does it include the cell?
Cells are consumables in every commercial agreement, and the warranty will say so. What matters is the boundary: a cell that fails at three months from a manufacturing defect should be covered, and a cell that fails at two years in normal service should not. Ask where the line is, and ask what the field return rate is. A supplier who will not state a return rate either does not measure it or does not want to.
12. Will the replacement cell exist in five years?
An instrument’s service life is longer than a cell’s. A supplier who cannot name the replacement part number, and cannot say how long that part will be produced, is selling an instrument with a hidden expiry date. This matters most for modules built into a customer’s product, where a discontinued cell means a redesign rather than a replacement.
How to use the list
Send all twelve in one email as a numbered list and ask for numbered replies. The content of the answers matters less than the shape of them.
A manufacturer answers most of them from documents they already have, and says “I do not know” to the rest with a date when they will. A trading company answers in prose, avoids the certification question, sends a catalogue instead of a register map, and offers a better price.
That difference is visible before the first sample ships, and it is not visible at all in a quotation.
Specific requirements, certification scope and document packages vary by market and by product. Nothing here is a substitute for checking a supplier’s certificates directly with the issuing body.