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

Abstract

The results obtained by five laboratories in the determination from dimensional measurements of the effective areas of two gas-operated 10 cm2 piston-cylinder assemblies are presented. These measurements were carried out as phase A1 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 Comité International des Poids et Mesures. The participants performed diameter, straightness and roundness measurements on each piston and cylinder bore and calculated the effective area of each piston-cylinder assembly using their own methods. The differences between diameters determined by the institutes are systematic and often greater than the uncertainties claimed by the participants. Nevertheless, all calculated effective areas agree with the reference values determined within the expanded uncertainties with a coverage factor 2, most of them even within their standard uncertainties. The choice of calculation method seems to be less important than the dimensional data themselves. The effective areas determined from the dimensional measurements are compared with those obtained in cross-float experiments with national pressure standards, in a comparison referred to as phase A2 and reported in a separate paper.

Calculation of effective areaA0for six piston–cylinder assemblies of pressure balances. Results of the EUROMET Project 740

“…The results for equation 5were the same as for equation (1). For the uncertainty evaluation, equation 1was transformed into a function of r 0 , r and R, given by equation 7in section 3.4.…”

“…The numeric integral value in equation (1) was calculated by Simpson's 3/8 Rule (for piston-cylinder units in liquid) and by a method for unequally segmented data (for pistoncylinder units in gas). The uncertainty of the effective area is expressed by:…”

“…The derivation of effective area A 0 (t ref , p atm ) of a pistoncylinder unit used in pressure balances is of great importance, representing the largest uncertainty contribution to pressure measurements. A CCM key comparison of methods used to derive A 0 was performed (CCM.P-K1a with data available on the KCDB of BIPM and [1]) using piston-cylinder units of high regularities. Despite the presence of a large diametrical variation in shape for one of the units of the comparison, the calculation results of participants were in excellent agreement.…”

Contributions of precision engineering to the revision of the SI

“…Fig. 46 shows the basic components of such a piston cylinder pressure gauge which serves as a reference for realisation of the pressure scale at the PTB [162,133].…”

A gas pressure scale based on primary standard piston gauges

“…Key Comparison CCM.P-K1c compared the standards of 5 NMIs from 79 kPa to 6.79 MPa during the time period from 1998 to 1999 [ 15 ]. NIST was the co-pilot of the comparison, which used two NIST piston gauge artifacts as the transfer standards.…”