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Fuel gas test bench for electronic domestic gas meters

On behalf and together with the Diehl Gas Metering GmbH, the Eng.-Office IMBUS developed in 2010 a world's new test bench for domestic electronic gas meters.

The development of such kind of test bench was necessary to be able to test and calibrate the electronic gas meters "AERIUS" based on the thermal measurement principle. In addition to the flow and temperature, the type of gas has to be adjusted and the measurement error of the meter has to be determined in relation to these three variables.

The two biggest challenges were the selection of the measurement standard and the handling of the fuel gases.

In this case, it is not possible to discharge the large amounts of fuel gases in the atmosphere, which are required for testing. This is neither environmental nor economic point of view possible. Therefore, a recycling system was developed, which regain the used fuel gas up on residual quantities. It is required, that after gas-replacement neither the gas of the test nor the recycled gas will have a purity deviance of more than 0.2 %.

These requirements depending on the different gases also have an impact on the usable reference standards. Piston- or bell prover have a large volume and not completely tight depending on the moving parts. The accuracy of drum type gas meters is critically through the sealing liquid. For these reasons it was decided to use venturi nozzles as reference standards.

So far venturi nozzles were not used as reference standards with fuel gases and small flows. In cooperation with the Technische Bundesanstalt (PTB), this technology was used and certified for the first time.

The test system consists of four main components:

_______________________  1. The thermal controlled test chamber

2. The nozzle block with valves and sensors  __________________

_____________________  3. The gas storage and recycling system

4. The PC control with I/O modules  _________________________

With the nozzles as a reference standard, the range of 14 l/h up to 10 m³/h is covered. In that way gas meters of the sizes G1.6 up to G6 can be tested. By a nozzles-staggering a continuous coverage of the whole flow range for gases from CH4 up to N2 with permissible deviations according to the PTB test rules is possible.

The combined uncertainty for the whole flow range and different gases and temperatures is approx. 0.65%.