CCM key comparison in the pressure range 0.05 MPa to 1 MPa (gas medium, gauge mode) - Phase A1: Dimensional measurements and calculation of effectivearea

The results obtained by five laboratories in the determination from dimensi onal measurements of the effective areas of two gas-operated 10 cm(2) pisto n-cylinder assemblies are presented. These measurements were carried out as phase Al of a key comparison in the pressure range 0.05 MPa to 1 MPa under the auspices of the Consultative Committee for Mass and Related Quantities (CCM) of the Comite International des Poids et Mesures. The participants p erformed diameter, straightness and roundness measurements on each piston a nd cylinder bore and calculated the effective area of each piston-cylinder assembly using their own methods. The differences between diameters determi ned by the institutes are systematic and often greater than the uncertainti es claimed by the participants. Nevertheless, all calculated effective area s agree with the reference values determined within the expanded uncertaint ies with a coverage factor 2, most of them even within their standard uncer tainties. The choice of calculation method seems to be less important than the dimensional data themselves. The effective areas determined from the di mensional measurements are compared with those obtained in cross-float expe riments with national pressure standards, in a comparison referred to as ph ase A2 and reported in a separate paper.