Validation of a PTB force-balanced piston gauge primary pressure standard

Ahmed Salama Hashad,Sven Ehlers,Wladimir Sabuga,Thomas Bock

doi:10.21014/acta_imeko.v10i1.821

Ahmed Salama Hashad, Sven Ehlers + Show 2 more

Open Access

https://doi.org/10.21014/acta_imeko.v10i1.821

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Abstract

Experimental methods using different pressure standards were applied to verify theoretical results obtained for the effective area of the piston-cylinder assembly (PCA) and for pressures measured with a force-balanced piston gauge (FPG). The theoretical effective area was based on the PCA’s dimensional properties defined via diameter, straightness and roundness measurements of the piston and cylinder, derived by gas-flow modelling using principles of the rarefied gas dynamics, and presented as two values: one obtained for absolute and the other for gauge pressure operation mode. Both values have a relative standard uncertainty of 5×10<sup>-6</sup>. The experimental methods chosen were designed to cover the entire operating pressure range of the FPG from 3 Pa to 15 kPa. Comparisons of the FPG with three different PTB pressure standards operated in different pressure ranges – a pressure balance, a mercury manometer and a static expansion system – were performed using the cross-float method and by a direct comparison of the generated pressures. For the theoretical and experimental effective area, as well as for pressures generated by the FPG and the reference standards, all the results demonstrated full agreement within the expanded uncertainties of the standards.

Highlights

Force-balanced piston gauges (FPGs) present an important class of piston gauge that enables pressure measurement from a few pascals to several tens of kilopascals
+ pR.rest + g h, where g is the local gravity acceleration, mi and ρi are the masses and their densities, respectively, ρamb is the density of the ambient gas, V is the piston’s additional volume with density ρl, Ar0 is the effective area of the Ruska pistoncylinder assembly (PCA), αr + βr is the thermal expansion coefficient of the Ruska PCA, pR.rest is the residual pressure in the Ruska bell jar and h is the height difference between the reference levels of the pressure balance and the FPG
The FPG was calibrated against the PTB mercury manometer (HgM), model 1025B made by Schwien Engineering (USA), which was modified at PTB and metrologically characterised, as described and validated in [25]-[26]

Summary

INTRODUCTION

Force-balanced piston gauges (FPGs) present an important class of piston gauge that enables pressure measurement from a few pascals to several tens of kilopascals. In these instruments, the force of the pressures acting on the piston of a pistoncylinder assembly (PCA) is measured by a high-accuracy balance. The force of the pressures acting on the piston of a pistoncylinder assembly (PCA) is measured by a high-accuracy balance This force and the effective area (A) of the PCA can be used to calculate the difference in the pressures above and below the piston [1], [2]. These standards have various operation principles and pressure ranges, as elaborated on below

EXPERIMENTS

Effective area determination

FPG vs mercury manometer

FPG vs static expansion system

RESULTS

CONCLUSIONS