Computation of the effective area and associated uncertainties of non-rotating piston gauges FPG and FRS

Abstract

The effective areas of three force-balanced piston gauges (FPGs) and two Furness Rosenberg standards (FRS) in the operating pressure range of each device varying for 1 Pa-15 kPa have been accurately computed both in the gauge and absolute modes.Geometrical data for the non-rotating piston-cylinder assemblies (PCAs) have been provided by the National Metrology Institutes (NMIs) of PTB, RISE, INRiM and CMI.Since the flow is in a wide range of the Knudsen number, simulations have been based on the Batnagar-Gross-Krook (BGK) kinetic model equation, while the typical Dadson and CFD approaches have been complimentary applied only in the viscous regime.Furthermore, an uncertainty analysis has been performed.The effective area is strongly affected by the PCA geometry and the flow conditions, while its dependency on pressure may be different even for devices of the same type.The main source of uncertainty is the dimensional measurements of the piston and the cylinder, followed by the accommodation coefficient characterizing the gas-surface interaction, while the effect of other flow and modeling parameters is negligible.The total relative standard uncertainty of the effective area has been always found to be less than 1 • 10 -5 indicating that pressure measurements of high accuracy can be ensured.Since the effective area is estimated based solely on computations the FPG and the FRS assemblies may be characterized as primary pressure standards.

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