Effective area calculation, uncertainty evaluation and studies for piston-cylinder units of non-ideal geometries used in pressure balances (extended pressure range)
Project Description
The derivation of effective area Ao (patm, tref) of a piston-cylinder used in pressure balances is of high importance representing the largest uncertainty contribution to pressure measurements. In the past a CCM key comparison of methods was performed (CCM.P-K1.a with data available on the KCDB of BIPM, G. Molinar et al, Metrologia, 1999, 36, 657-662) using piston-cylinder units of high regularities, and even in presence of a large change in its form during the comparison the calculation results of participants were in good agreement.
The purposes of this new projects would be:
- to initially select at least five units, with already available full dimensional characterization of piston and cylinder, but intentionally having non ideal conditions (possibly large irregularities but for units that are really in use as primary standards in the partners laboratories) of the shape of piston and cylinder and having different diameters for a use in pressure balances from few MPa to 1 Gpa full scales
- to compare the values of Ao (patm, tref) derived by each participant including the evaluation of its uncertainty u (Ao) and possibly to recommend the best suitable methods of calculation
- to study some key points particularly in the inlet and outlet cylinder zone where dimensional measurements are difficult to be made, and to evaluate the applicability and restriction of the axis-symmetric model used
The participants are asked to perform calculations following their traditional methods, using as well FEM calculations if available.
The projects is aimed to obtain results in about one year from the start; strict cooperation & rsquo;s between partners (including as well possibilities of involving sub-partners) is essential to reach the objects of the project. Dimensional data of the piston-cylinder units should be available at starting date.
Final Report 2005-03-04
The project has been completed and results are available in Metrologia doi.org/10.1088/0026-1394/42/6/S11.
The derivation of effective area Ao (patm, tref) of a piston-cylinder used in pressure balances is of high importance representing the largest uncertainty contribution to pressure measurements.
The purposes of this projects has been based on:
- a selection of six piston-cylinder units, with full dimensional characterization of piston and cylinder, intentionally having non ideal conditions of the shape of piston and cylinder and having different diameters for a use in pressure balances from few MPa to
1 Gpa full scales in gas and liquid media - the comparison of the values of Ao (patm, tref) derived by each participant including the evaluation and comparison of its standard uncertainty u (Ao)
- the study of some key points (inlet and outlet cylinder zone where dimensional measurements are difficult to be made, applicability and restriction of the axis-symmetric model, …)
The participants performed calculations following their traditional methods, and a full description of selected units, calculation methods used by participants, analysis of the results have been approved by all participants and are given in [1].
A paper [2] will be presented to the 4th CCM International Pressure Conference, London, UK, 19-21 April 2005 and will be submitted for publication to Metrologia (Proceedings of the 4th CCM Pressure Conference).
[1] G. Molinar et al, Final Report EUROMET Project 740, Calculation of effective area Ao of six piston-cylinder units of pressure balances, File: 740_Final_Report_January_05.doc, 20 January 2005
[2] G. Molinar, M. Bergoglio, W. Sabuga, P. Otal, G. Ayyildiz, J. Verbeek and P. Farar, Calculation of effective area Ao of six piston-cylinder units of pressure balances. Results of the EUROMET Project 740, to be submitted to “Metrologia” in the Proceedings of the 4th CCM International Pressure Conference, London, UK, 19-21 April 2005