scope:

This Standard is not intended to be used in conjunction with high accuracy meter installations where, for example, flow computers are configured to receive live data of gas composition. Such installations are the subject of other standards, for example IGEM/GM/8 and IGEM/GM/4 and, as appropriate, national and international standards.

Note: Typical functions provided by conversion devices and flow computers are given in Table 1.

This Standard covers installation (including appropriate pre-installation tests), commissioning, validation, monitoring and maintenance of conversion devices and advanced meters that convert gas volume readings to base conditions by taking into account temperature, pressure and, if appropriate, compressibility of the gas. This Standard covers pressure not exceeding 38 bar.

Note 1: Normally, the conversion devices referred to in this Standard are battery powered, whereas flow computers are mains powered.

Note 2: A typical volume conversion system is shown in Figure 1.

Note 3: In general conversion devices are not used at operating pressure (OP) exceeding 7 bar (when a flow computer is used).

Note 4: Conversion devices are sometimes referred to as EVCS, EVCD, volume converter and occasionally volume corrector.

The conversion devices covered by this Standard usually process low frequency (LF) pulsed signals from a LF transmitter within, or external to, a meter, together with other inputs to provide a digital display of converted volume. However, there are options available to improve the reliability of systems by the use of alternative data encoders, electronic indexes, and fully integrated meters with volume conversion and automatic meter reading (AMR) capabilities, and these are also covered by this Standard.

Density correction is outside the capability of such conversion devices and the scope of this Standard.

Note 1: Traditionally, meters have been supplied with pulse generation created by a magnet incorporated in the index mechanism and a magnetically-operated switch (usually, a reed switch). However, some more modern meters use optical sensing or electronic sensors of other forms. While many of these are compatible with the conversion devices available, care has to be taken to ensure that this compatibility is demonstrated and, where appropriate, correct polarity is observed when making electrical connections to these assemblies.

Note 2: IGEM/GM/7A provides guidance on all electrical connections to gas meters.

Note 3: In general, flow computers process high frequency (HF) pulsed signals.

Note 4: Further details on flow computers are contained in IGEM/GM/4.

This Standard covers volume conversion systems that are independent of the physical meter, however, at the users discretion the principles of this document may be applied to meters with integral volume conversion systems.

The conversion systems covered by this Standard may be designed for installation in either indoor or outdoor environments.

This Standard, although not intended to form a specific site procedure, can, nevertheless, be used as the basis for such a procedure.

This document includes limited guidance on other areas where EVCSs are being applied. This guidance covers circuits for additional data applications, e.g. customer data acquisition systems.

Pressures quoted are gauge pressures unless otherwise stated.

Italicised text is informative and does not represent formal requirements.

Appendices are informative and do not represent formal requirements unless specifically referenced in the main sections via the prescriptive terms "must", "shall" or "should"