S-G-03–Specifications for the approval of type of gas meters, ancillary devices and associated measuring instruments

Category: Gas
Issue date:
Effective date:
Revision number: 1
Supersedes: LMB-EG-08 and S-G-03


Part 2: Diaphragm meters

Table of contents


1.0 Scope

This part of the Specifications applies to positive displacement diaphragm type gas meters submitted for approval.

2.0 Definitions

Apparent rated capacity (QA) (capacité nominale apparente)

Air flow rate through the meter at atmospheric pressure and relative humidity as specified in Part 1, 12.2.1, which produces a pressure drop of 125 Pa (0.5 inches of water) across the meter when the inlet pressure at the meter is 500 Pa (2 inches of water).

Declared rated capacity (capacité nominale déclarée)

Volume flow rate of air with 125 Pa (0.5 inches of water) differential across the meter at 101.325 kPa (14.73 psia) and 15 °C (60 °F) as established and declared by the manufacturer.

Diaphragm meter (compteur à parois déformables)

A volume measuring gas meter (positive displacement type) in which the measurement of the gas flow is effected by means of measuring chambers with deformable walls.

Low load registration test (essai de l'enregistrement à faible charge)

Performance test that determines the flow rate of air at which the meter starts to register continuously.

Non-temperature-compensated meter (compteur sans compensation de la température)

A diaphragm meter fitted with a "standard tangent", which is not designed to provide a base temperature-converted volume registration.

Temperature-compensated meter (compteur à compensation de température)

A temperature-converted diaphragm meter, more commonly referred to as a temperature-compensated meter. Diaphragm meters equipped with a temperature converting tangent are designed to produce a volume registration which has been converted to a base temperature of either 15 °C (for cubic meters) or 60 °F (for cubic feet).

3.0 Metrological requirements

The applicable requirements of Part 1, section 7.0 shall apply unless otherwise stated in this section.

3.1 Flow rate characteristics

The terms Qmin, Qt and Qmax are not applicable.

3.2 True rated capacity

Where the density of air used to establish the apparent rated capacity (QA) differs from the density of dry air at standard conditions, the following formula shall be used to convert the QA to the true rated capacity of the meter:

(Q t) = (Q A) × (((d t) ÷ (d b))^0.5)

where,

3.3 Registration

3.3.1 Low load registration

With the meter inlet pressure at 500 Pa (2 inches of water), the meter shall start to register continuously at a flow rate not greater than 1% of its declared rated capacity.

3.3.2 Maximum permissible errors

The following MPEs shall apply to the volume registration (see Part 2, Table 1).

Part 2, Table 1: Diaphragm meter maximum permissible errors
Flow rates (Q) Working pressure (pw) Test conditions MPE
5% ≤ Q ≤ 200% of the true rated capacity  500 Pa (2 in H2O) ≤ pwPmax Reference ± 1%
"Other than reference" Non-temperature-compensated meter ± 1.5%
Temperature compensated meter ± 2%
3.3.3 Meter calibration

Meters selected for the evaluation of metrological requirements shall be calibrated by the manufacturer at 25% and 150% of the declared capacity within an error not greater than ± 0.5% at these test points or a spread between the test points less than 0.5%.

4.0 Technical requirements

The applicable requirements of Part 1, section 8.0 shall apply unless otherwise stated in this section.

4.1 Design and construction

Temperature compensated diaphragm meters are exempt from the requirements in Part 1, 8.1.4 and Part 10.

4.2 Mechanical indicating device

In addition to the applicable requirements mentioned in Part 13, subsection 2.1, the volume capacity of the proving dials or drums and test dial shall correspond to an integral number of complete revolutions of the primary measuring mechanism of the meter.

4.3 Output shaft

Where a meter is equipped with an external output shaft that can drive an ancillary device, the volume capacity per revolution of the shaft shall correspond to an integral number of complete revolutions of the primary measuring mechanism of the meter.

5.0 Marking requirements

In addition to the applicable requirements of Part 1, section 9.0, the following shall apply.

5.1 The manufacturer's rated capacity of air shall be marked on the nameplate and shall not exceed the true rated capacity as determined in subsection 3.2.

5.2 The manufacturer of the diaphragm shall be marked on the diaphragm in such a location that the marking is visible when the diaphragm assembly is in place.

6.0 Performance tests

The applicable requirements of Part 1, section 12.0 shall apply unless otherwise stated in this section.

6.1 Test conditions

6.1.1 Operating conditions
6.1.1.1 Reference and "other than reference" working pressures (pw)

The flowing gas pressure shall be any pressure from 500 Pa (2 inches of water) up to the maximum allowable operating pressure (Pmax) for which approval is being sought.

6.1.2 Flow rate test points

The flow rates (Q) shall be between 5% and 200% of the true rated capacity.

6.2 Evaluation tests

6.2.1 The following tests shall be conducted at reference conditions:

  1. Tests to confirm apparent rated capacity;
  2. Low load registration tests where the meter inlet pressure shall be 500 Pa (2 inches of water);
  3. Load registration tests where flow rates shall be distributed over the measuring range specified in 6.2.1 at a working pressure as specified in 6.1.1.1 (see Part 2, Table 2).

6.2.2 At "other than reference" conditions, load registration tests shall be conducted as specified in 6.3.1(c) (see Part 2, Table 2).

Part 2, Table 2: Diaphragm meter accuracy testing
Flow rates (Q) Working pressure (pw) Working temperature (tw) Environmental conditions
5% ≤ Q ≤ 200% of the true rated capacity 500 Pa (2 in H2O) ≤ pwPmax     Reference Reference
"Other than reference" "Other than reference"

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