Certifying a gas-meter power source means satisfying three examiners at once: the metrologist checking that billing stays accurate as the battery ages, the ATEX assessor checking that no electrical fault can ignite gas, and the safety engineer checking that the shut-off valve still closes at year ten in the cold. This paper layers that evidence for a primary-lithium-plus-NiMH design, mapping each test to EN 1359, OIML R137, MID, the ATEX standards and the cell-level IEC and UN evidence.
EN 1359 and OIML R137 define the gas-meter accuracy and durability requirements, and MID governs legal-metrological conformity. The battery test must demonstrate that measurement error stays within limits from a fresh cell to the end-of-life voltage, that the non-volatile totaliser never loses or invents consumption, and that a low battery raises an alarm while metrology continues unaffected. The shut-off decision logic is also tested: the meter must distinguish genuine abnormal-flow events from low-battery behaviour.
Running the metrological accuracy programme at fresh, mid-life and end-of-life battery states, and at the temperature extremes, closes the risk that a weakening battery corrupts the legal measurement.
ATEX Directive 2014/34/EU and the IEC 60079 series (notably the general requirements and the intrinsic-safety standard 'i') govern equipment in explosive atmospheres. The battery and pulse reservoir are assessed as potential ignition sources: maximum open-circuit voltage, short-circuit current, stored energy and surface temperature under normal and single-fault conditions, with the protection components and their ratings documented. The hybrid design's current-limited, fused NiMH reservoir is evaluated within the same intrinsic-safety barrier as the primary cell.
The test record includes the ignition-curve assessment for the relevant gas group, temperature-class verification, and confirmation that opening the meter for the (sealed) battery does not expose an incendive circuit - evidence that favours a small, well-defined, aqueous reservoir over an unconstrained energy store.
Gas meters see -25 to +55 C, condensation and IP65-IP67 environments. The validation combines temperature cycling and soak with the valve-pulse test, because the guaranteed close is hardest at the cold extreme with an aged reservoir. Ingress and corrosion testing verifies welded tabs and potting against years of humidity, and vibration testing reflects meter installation and transport.
NiMH's ability to discharge below freezing (while respecting its no-charge-below-zero limit) and its sealed, welded construction are verified here, alongside the primary lithium's cold behaviour, so the combination - not either cell alone - is proven for the environment.
IEC 62133-1 covers sealed nickel-system cell safety (Part 1) and IEC 61951-2 the performance methods including charge retention and the >=500-cycle endurance reference; UN 38.3 covers transport. The primary lithium cell carries its own lithium safety and transport evidence, kept distinct in the file. A practical logistics point: NiMH service and replacement packs ship without lithium-air restrictions, simplifying field-depot supply.
The interaction of the two chemistries is also documented, proving the charging path cannot overcharge or reverse the reservoir and that a reservoir fault cannot pull the primary cell outside its safe envelope.
The most predictive test compresses a decade: thousands of daily radio cycles at the measured current, monthly (and worst-case daily) valve cycles, temperature soak between, and continuous tracking of the reservoir's delivered voltage under the valve load. The second animated figure contrasts the guaranteed valve-pulse capability over the simulated decade at a mild versus a cold operating profile, showing how disciplined sizing and gentle charging preserve the safety action while an under-sized or heat-stressed reservoir loses it.
This programme, combined with primary-lithium discharge and passivation tests, validates the two field-failure modes that matter most: a daily report that cannot get through, and - non-negotiably - a shut-off valve that cannot be guaranteed to close.
Assemble the EN 1359/OIML R137 accuracy-across-voltage record, the MID file, the ATEX intrinsic-safety assessment with fault analysis, the environmental and ingress report, the IEC 62133-1 and IEC 61951-2 nickel certificates, the primary-lithium evidence, the UN 38.3 summaries and the decade valve-pulse ageing results. That dossier is what a gas network, a notified body and an ATEX assessor need to approve the meter.
Specifying an intrinsically safe, aqueous NiMH pulse reservoir at the design stage is the most direct route to a meter that reports for a decade and - when it matters most - closes without fail.
Weijiang Power manufactures sealed nickel-metal hydride cells and pulse-assist modules for smart gas meters and safety shut-off actuators. Send us your radio profile, valve motor current and travel time, ATEX category and temperature class, and our engineers will design an intrinsically safe, welded NiMH pulse reservoir or service module matched to the primary lithium cell. See formats on the products page.
