Abstract
This paper describes a volume comparison method carried out under a fine/rough vacuum using a small transfer flow rate from a capillary leak artefact. This method is suitable for volumes of vessels with complex shapes such as tubing arrangements equipped with various pneumatic parts (valves, gauges …), sample volumes, etc. The calibration, based on pressure rise measurements performed with a constant-volume flowmeter set-up, exhibits a standard relative uncertainty between 0.03 % and 2 % for volumes ranging from 1 to 3000 cm³, which is only about one order of magnitude higher than capabilities of the gravimetric volume calibration.
Highlights
The most accurate way to determine the volume contained by a vessel is the so-called “gravimetric volume calibration” method [1], which consists in weighing the vessel, empty and filled with a liquid and calculating the volume from the mass and density of the liquid added
It is derived from the pressure rise method implemented in the Laboratoire commun de métrologie (LCM LNE-Cnam) constant-volume flowmeter [2] used to calibrate leak rates in the range from 1×10-7 to 1×10-2 Pa·m3·s-1
The volume calibration using a comparison method with a transfer leak flow rate was originally developed for the needs of companies owning sample volumes in which some gas is trapped for a further analysis. As this kind of artefact is sometimes incompatible with the gravimetric volume calibration and has to be functionally tight to a certain extent, the comparison method is well suited
Summary
The most accurate way to determine the volume contained by a vessel is the so-called “gravimetric volume calibration” method [1], which consists in weighing the vessel, empty and filled with a liquid (usually water) and calculating the volume from the mass and density of the liquid added. The comparison method presented here is suited to volumes either incompatible with liquids or else with internal shapes such that prevent complete filling It is derived from the pressure rise method implemented in the Laboratoire commun de métrologie (LCM LNE-Cnam) constant-volume flowmeter [2] used to calibrate leak rates in the range from 1×10-7 to 1×10-2 Pa·m3·s-1. The leak rate is deduced from the measured pressure rise rate and the total volume into which the gas flows In this flowmeter, a standard volume, calibrated using the gravimetric method, is connected in series with the internal volume of the tubing which links the leak artefact to the pressure sensor, called the dead volume. A standard volume, calibrated using the gravimetric method, is connected in series with the internal volume of the tubing which links the leak artefact to the pressure sensor, called the dead volume This latter may be determined prior to the leak rate measurement. As this kind of artefact is sometimes incompatible with the gravimetric volume calibration and has to be functionally tight to a certain extent, the comparison method is well suited
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