S-G-03–Specifications for the approval of type of gas metering devices–Part 13

Category: Gas
Issue date:
Effective date:
Revision number: 3
Supersedes: S-G-03 (rev. 2)


Part 13: Electronic gas metering devices incorporating correction and linearization functions

Table of contents


1.0 Scope

This part of the Specifications provides the requirements for the approval evaluation of meter performance enhancement schemes based on the linearization or curve fitting of uncorrected or raw flow calibration data. It applies to schemes which are incorporated in the following devices that are intended to be user accessible and programmable at the time of initial verification:

  • flow computers;
  • devices incorporating correction functions;
  • gas meters; and
  • supporting software external to the device.

This part must be read in conjunction with the specifications particular to each type of device.

Note: The following two types of meter performance enhancement schemes are addressed in this part:

  • The selection of K factors or gas meter factors as a function of flowrate and,
  • The selection of correction factors based on input parameters (i.e. 4-20 mA inputs from transmitters).

2.0 Metrological requirements

2.1 General

The following requirements must apply:

  • Prior to correction, the error of the device where the correction function resides must not exceed the MPE for device.
  • The error correction must not exceed the MPE for the device where the correction function resides.
  • The error correction and correction factor applied must not exceed ± 0.1% of the error and the correction factor as determined in accordance with the correction method for which approval is sought.
  • Correction for flow rates or input parameters below the minimum test point for which an error has been established must be the correction established at the minimum test point.
  • Correction for flow rates or input parameters above the maximum test point for which an error has been established must be the correction established at the maximum test point.

2.2 Error correction methods

Correction for a known error must be based on one of the following methods.

2.2.1 Linear interpolation (point-to-point linearization)

The following requirements must apply:

  1. The error between adjacent predetermined calibration values must be determined in accordance with the equation for a straight line ( Y = mX + b ) .
  2. The meter performance correction values (either meter factors or K factors) must:
    • be based on the error as determined for the current flow rate or input parameter as applicable;
    • be used to correct the raw meter pulse signal or input parameter; and
    • provide an estimate of the true value of flow or input parameter as applicable.
2.2.2 Modelling equation

The following requirements must apply:

  1. A modelling equation (such as a fourth-order equation) that results in a series of coefficients (a, b, c, d, e, etc.) and an estimate of the uncertainty of the curve fit being provided must be used.
  2. The equation coefficients specified in a must be programmed into the device where the correction function resides.
  3. Corrections must be calculated using the same equation, by the devices in which the correction function resides, and used to correct the metering measurement unit or input parameter and provide an estimate of the true value of flow or input parameter.
2.2.3 Discrete step interpolation

The error between adjacent predetermined calibration values must be the calibration value determined at the lower percentage of the range for the device and the requirements specified in 2.2.1 b must apply.

3.0 Technical requirements

All parameters which are not measured but are necessary for correcting must be contained in the device where the correction function resides before any measurement operation is carried out. The device performing the correction must be able to display or communicate the following information which must reside in it:

  • Each test point at which the device was tested and the error at the test point;
  • The current flow rate or input parameter being used by the correction function;
  • The correction factor applied as determined by the correction function.

4.0 Performance test requirements

Note: Test conditions and performance tests can be obtained by contacting MC.

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