S-G-03–Specifications for the approval of type of gas meters, ancillary devices and associated measuring instruments
Revision number: 1
Supersedes: LMB-EG-08 and S-G-03
Part 18: Correction function of gas meters
Table of contents
- 1.0 Scope
- 2.0 Metrological requirements
- 3.0 Technical requirements
- 4.0 Performance tests
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.
This part applies to schemes which are incorporated in flow computers, correction devices, flow meters and supporting software external to the measuring instrument, and are intended to be user accessible and programmable at the time of initial verification.
This section shall be read in conjunction with the specification to each type of meter and ancillary device in subsequent sections specific thereto.
2.0 Metrological requirements
2.1.1 Prior to correction, the error of the measuring instrument where the correction function resides shall not exceed the MPE for themeasuring instrument.
2.1.2 The error correction shall not exceed the MPE for the measuring instrument where the correction function resides.
2.1.3 The error correction and correction factor applied shall not exceed ± 0.1% of the error and the correction factor as determined in accordance with the correction method for which approval is sought.
2.1.4 Correction for flow rates or input parameters below the minimum test point for which an error has been established shall be the correction established at the minimum test point.
2.1.5 Correction for flow rates or input parameters above the maximum test point for which an error has been established shall be the correction established at the maximum test point.
2.2 Error correction methods
Correction for a known error shall be based on one of the following methods.
2.2.1 Linear interpolation (point-to-point linearization)
220.127.116.11 The error between adjacent predetermined calibration values shall be determined in accordance with the equation for a straight line ().
18.104.22.168 The meter performance correction values (either meter factors or K factors) shall be based on the error as determined for the current flow rate or input parameter as applicable.
22.214.171.124 The values specified in 126.96.36.199 shall 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 Modelliing equation
188.8.131.52 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 shall be used.
184.108.40.206 The equation coefficients specified in 220.127.116.11 shall be programmed into the device where the correction function resides.
18.104.22.168 Corrections shall 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 Discreet step interpolation
22.214.171.124 The error between adjacent predetermined calibration values shall be the calibration value determined at the lower percentage of the range for the measuring instrument.
126.96.36.199 The requirements specified in 188.8.131.52 and 184.108.40.206 shall apply.
3.0 Technical requirements
3.1 All parameters which are not measured but are necessary for correcting shall be contained in the device where the correction function resides before any measurement operation is carried out.
3.2 The device performing the correction shall be able to display or communicate the following information which shall 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 tests
4.1 As a minimum, the applicant shall conduct the following tests and submit the test results with the application:
- A performance test below the minimum test point for which a known error has been established.
- A performance test above the maximum test point for which a known error has been established.
- Performance tests at different test points, between the minimum and maximum flow rates or input parameters for which approval is sought.
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