A constant pressure gas flowmeter using a directly driven diaphragm bellows as a volume displacer was studied. This flowmeter is perfectly vacuum-sealed, does not contain elastomers and liquids that would prevent outgassing at elevated temperatures and can achieve a smaller ratio of the final volume to the displaced volume than when bellows are used, so that the uncertainty in generating small flow rates can be small. As, when a bellows is used in the volume displacer, the displaced volume cannot be calculated from the geometric dimensions and its dependence on the displacement is non-linear, a sensitive method had to be developed for measuring this dependence. The uncertainty in measuring the displaced volume by this method and the achieved uncertainty of the flowmeter were determined.

This report describes a EURAMET comparison of five European National Metrology Institutes in low gauge and absolute pressure in gas (nitrogen), denoted as EURAMET.M.P-K4.2010. Its main intention is to state equivalence of the pressure standards, in particular those based on the technology of force-balanced piston gauges such as e.g. FRS by Furness Controls, UK and FPG8601 by DHI-Fluke, USA. It covers the range from 1 Pa to 15 kPa, both gauge and absolute. The comparison in absolute mode serves as a EURAMET Key Comparison which can be linked to CCM.P-K4 and CCM.P-K2 via PTB. The comparison in gauge mode is a supplementary comparison.

This report describes pressure comparison measurements in the range 0.07 MPa to 0.4 MPa between the Czech Institute of Metrology (CMI) and the Physikalisch-Technische Bundesanstalt (PTB) in the period 9 to 13 March 1998 at the Pressure Section of the PTB, Braunschweig. The transfer standard used was a gasoperated piston-cylinder assembly with a ceramic piston of nominal effective area 10 cm 2 and a tungsten-carbide cylinder, installed in a pressure balance base unit, model PG 7601, manufactured by DH Instruments, USA. The measurements compare the effective area of the transfer piston-cylinder assembly as determined from dimensional data at the CMI with effective area data obtained from pressure measurements (i) in gauge mode with the primary standard pressure balance and (ii) in absolute and gauge mode with the primary standard dual-cistern mercury manometer of the PTB. Both primary standard instruments have been used in the international comparison measurements organized by the Consultative Committee for Mass and Related Quantities (CCM) of the Comité International des Poids et Mesures. It may be seen that geometrical measurement values of the effective area agree with results from the PTB and that the relative difference between the effective area is minimal: for the standard pressure balance, 3.4 10 -6 for absolute pressure, 3.4 10 -6 for gauge pressure; and for the dual-cistern mercury manometer, 1.8 10 -6 for gauge mode. The relative difference between the experimental absolute and gauge mode for the dual-cistern mercury manometer is 1.5 10 -6 .

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