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DRAFT⚠OIML SMART pilot programme · internal use only · all documents and specifications are drafts and may change without notice
OIML SMART

OIML R 144: Diaphragm gas meters

Diaphragm gas meters are the workhorses of residential and commercial gas metering, measuring fuel gas consumption for billing. R 144 specifies the metrological requirements that ensure those measurements are accurate and auditable.

Scope

OIML R 144:2006 specifies requirements for diaphragm gas meters, the positive-displacement instruments used to measure fuel gases. It covers:

  • Meter sizes from G1.6 to G100 (rated flow capacity).
  • Accuracy classes: 1.0, 1.5, 2.5.
  • Pressure ranges, temperature ranges.
  • Construction, marking, and test report format.

What’s modelled

Layer Count
Requirements 28
Conformance tests 11
Forms 8
Terminology ~45

Headline tests

  • Measurement error (R 144 §5.1), error vs reference flow rate across the rated flow range, including the Qmin to Qt transition zone.
  • Pressure loss (R 144 §5.2), pressure drop across the meter at rated flow.
  • Cyclic volume (R 144 §5.3), verifies the meter’s per-cycle displaced volume matches its rating.
  • Temperature effect (R 144 §5.4), measurement accuracy across the rated temperature range.
  • Endurance test (R 144 §5.5), long-duration cycling to verify sustained accuracy.

Computation: MPE zone transitions

Diaphragm gas meters have a two-zone MPE structure:

  • Lower zone (Qmin to Qt), larger tolerance, typically ±3%.
  • Upper zone (Qt to Qmax), tighter tolerance, typically ±2% (class 1.5).

The transition flow Qt is declared per meter size. The MPE form looks up the correct tolerance band based on the actual flow rate:

table: r144_mpe_table
kind: range
inputs:
  - name: meter_size   # G1.6, G2.5, G4, G6, G10, G16, G25, G40, G65, G100
    type: enum
  - name: flow_rate
    type: numeric
    unit: m3/h
output:
  name: mpe_pct
ranges:
  - when: { meter_size: G4, flow_rate: [0.04, 0.4] }    # Qmin to Qt
    value: 3.0
  - when: { meter_size: G4, flow_rate: [0.4, 6.0] }     # Qt to Qmax
    value: 2.0
  # ...

Explore the model

Certification path

Certification of diaphragm gas meters follows the standard workflow. Manufacturers typically submit multiple samples (3–6) of each model to cover production variability.