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Title: An Intercomparison Between Primary High-Pressure Gas Flow Standards With Sub-Permille Uncertainties
Author: Jos G.M. Van Der Grinten, Arnthor Gunnarsson, Mijndert Van Der Beek, Bodo Mickan
Source: 2019 North Sea Flow Measurement Workshop
Year Published: 2019
Abstract: Currently, state-of-the-art commercial calibrations of high-pressure gas flowmeters are performed with uncertainties that range between 0.13% and 0.25%, depending on pressure and flowrate.These measurement capabilities are traceable to primary standards using several steps in which the flowrate range and pressures are increased. For the primary high-pressure calibration facilities in Western Europe these traceability chains are described in 1. In France a pVTt tank is used, in The Netherlands, Germany and Denmark piston provers are used. The National Metrology Institutes and Designated Institutes of these countries cooperate with the high-pressure calibration laboratories in the EuReGa consortium (European References for Gas). Every three years, after recalibration of the participants high-pressure gas flow laboratories, EuReGa organises an intercomparison at the level where commercial calibrations are performed. These results are used to average the traceability chains of the laboratories, which also results in lower uncertainties. This process is called harmonisation and the procedure and data processing is described in 2.The results of the harmonisation exercises are reported by EuReGa 3. In the past 20 years of harmonisation the differences between the laboratories have diminished and the uncertainties have improved 2.After the success of20 years of intercomparisons, EuReGa extends the intercomparisons to the level of the primary standards. These are operated with sub-permille uncertainties, i.e. with expanded uncertainties (??2) better than 0,1%. Unfortunately, the French colleagues cannot participate. Their primary pVTt tank operatesat variable pressure. For the pVTt tank critical flow Venturi nozzles (sonic nozzles) are suitable as intercomparison devices as their mass flowrate does not depend on the downstream pressure. An intercomparison between LNE-LADG, PTB, NIM and NIST using sonic nozzles4, demonstrated the equivalence of the French and the German primary standards.The two DN100 turbine gas meters used in this comparison have been used in previous EuReGa intercomparisons. The last time in 2017 -20183. In this paper these results will be compared with the present results utilising piston provers.

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