EXPERIENCE WITH GRAVIMETRIC FLOW STANDARD (GFS) IN VACUUM AND HERMETIC MODE

Zdeněk Krajíček, Martin Vičar, Dominik Pražák, Jiří Tesař, Tomáš Hajduk, Ladislav Peksa, Tomáš Gronych, Martin Jeřáb

Abstract

The Czech national standard of low gas flow is based on a gravimetric flow standard (GFS) principle. It means it defines the flow as the mass loss of gas from a pressure bottle which is continuously weighed. This weighing is performed in an ambient atmosphere which causes that the main source of uncertainty results from the buoyancy correction. This buoyancy correction is complicated by the instabilities of the atmospheric environment and by the fact that volume of the weighed pressure bottle is dependent both on temperature and internal pressure. By modifying the experimental set-up of the GFS utilizing weighing in vacuum, it is possible to suppress the problematic buoyancy effects and moreover to eliminate other impractical side effects such as water vapour condensation on the pressure bottle due to cooling below dew point for the higher flow rates. This presentation describes the practical problems of the vacuum modification of the GFS together with the uncertainty analysis of the modified experimental set-up and the measurement results. The hermetic mode and its main applicability is also introduced.

Keywords

equivalence of national standards, flow metrology, gravimetric flow standard

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IMEKO-WC-2015-TC9-220.pdf

DOI

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IMEKO TC

TC9 - Flow Measurement

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