Realisation of the Unit of Gas Volume
The standard instrument for the realisation of gas volume at BEV is a bellprover with a content of 500 litres, the content being divided into 10 segments of 50 litres each.
The actual content of the segments is determined volumetrically, i.e. through displacement of a liquid in a capacity measure. Air flow rates from 0.02 m³/h to 25 m³/h can be produced with a bellprover, the pressure being close to ambient pressure.
Four rotary piston gas meters in a test rig constitute the national flowmetering facility for high flow rates. Gas meters with a flow rate up to 1000 m³/h can be calibrated with this test rig. Ambient pressure air is used as the test medium. The standard instruments with flow rates over 25 m³/h are calibrated on a regular basis at Nederlands Meetinstituut (NMi), Netherlands, or at Physikalisch-Technische Bundesanstalt (PTB), Germany.
Volume Conversion Devices
Volume conversion devices are auxiliary devices of large gas meters. They convert the volume measured by the gas meter at working conditions into a volume at standard conditions (1.01325 bar and 0 °C).
Verification of Gas Meters and Volume Conversion Devices
Gas meters and volume conversion devices are subject to mandatory verification in Austria. The first verification of a new instrument is called initial verification. The verification of an unverified instrument is a new verification. Verification during the validity period is a reverification.
The Measuring Instruments Directive (MID) has been applied in all EU Member States since October 30, 2006 regulating the first placing on the market of measuring instruments subject to mandatory verification. These measuring instruments have to undergo a conformity assessment procedure. Gas meters and volume conversion devices are included in the MID. Therefore measuring systems with a conformity certificate can be put into use without any further national type approval or initial verification.
The conformity assessment is equivalent to the initial verification.
Modules B+D, B+F, and H1 are the conformity assessment procedures applicable to gas meters and volume conversion devices.
New and initial verification of gas meters and volume conversion devices are regulated by national regulations and carried out by accredited verification bodies.
The reverification period for diaphragm gas meters is 12 years, for volume conversion devices 5 years, whereas turbine and rotary piston gas meters are exempted from reverification.