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A new controlled-clearance (CC) pressure balance has been developed with the aim of improving hydraulic pressure standards up to pressures of 1 GPa. The pressure balance is equipped with a weight-loading unit that can load/unload selected weights automatically and a CC piston-cylinder that is designed for the jacket pressure to be applied independently. In this paper, the effective area A(e) of two kinds of the CC piston-cylinders for pressures of 200 and 500 MPa was examined based on the Heydemann-Welch model. The two parameters in the model, the jacket pressure coefficient and the zero clearance jacket pressure, were precisely determined by the characterization experiments, after which the pressure dependence of A(e) and its uncertainty were estimated. The uncertainty due to the pressure dependence of A(e) for the 500 MPa CC piston-cylinder was less than 7.5x10(-8) MPa(-1). To confirm the consistency of the estimations, the results of the two CC piston-cylinders were compared through a free-deformation (FD) piston-cylinder; the two estimations were in agreement with each other. Moreover, it was shown that the extent of nonlinearity in the pressure dependence of A(e) of the FD piston-cylinder can be evaluated by calibration against the CC piston-cylinder.

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This report describes the results of a supplementary comparison of hydraulic high-pressure standards at two national metrology institutes (NMIs) – National Metrology Institute of Japan, AIST (NMIJ/AIST) and Physikalisch-Technische Bundesanstalt (PTB), Germany – which was carried out during the period January 2007 to March 2007 within the framework of the Asia-Pacific Metrology Programme (APMP) and the European Association of National Metrology Institutes (EURAMET) in order to determine their degrees of equivalence at pressures in the range 100 MPa to 1000 MPa for gauge mode.The pilot institute was NMIJ/AIST. NMIJ/AIST used a hydraulic pressure balance and a pressure multiplier, and PTB used a controlled-clearance pressure balance as their pressure standards. High-precision pressure transducers were used as a transfer standard. The sensing element of the transducers was a foil strain gauge. To ensure the reliability of the transfer standard, two pressure transducers were used on the transfer standard unit. At the beginning and the end of this comparison, the transfer standard was calibrated at the pilot institute.From the calibration results, the behaviour of the transfer standard during the comparison period was characterized and it was found that the capability of the transfer standard for the purpose of this supplementary comparison was sufficient. The degrees of equivalence of the national measurement standards were expressed in terms of deviations from the supplementary comparison reference values and from each other, considered in combination with associated uncertainties of these deviations. The hydraulic pressure standards in the range 100 MPa to 1000 MPa for gauge mode of the two participating NMIs were found to be equivalent within their claimed uncertainties.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Deformational characteristics of a controlled-clearance piston-cylinder (CCPC) have been evaluated to precisely estimate the pressure dependence of its effective area. Among the experimentally accessible characteristics, the jacket pressure coefficient d, which denotes the relative change in the effective area due to applied jacket pressure pj, is examined in this paper. Two methods for precisely determining d at pressures up to 1 GPa are proposed. One is a comparative method that uses a set of a pressure balance and a multiplier as the tare gauge. The other is a new method that uses precise pressure transducers as monitoring devices. Both pj and weights loaded on the CCPC are changed so that the pressure generated by the CCPC remains constant, which is monitored by the transducers. d is estimated by the relative change in the weights loaded on the CCPC itself. Using the two methods, d for a 1 MPa kg−1 CCPC is measured at pressures up to 1 GPa. At each system pressure, d obtained by each method is approximated by a linear function of pj. The consistency of the fit values of d by the two methods is confirmed. The method using pressure transducers as monitoring devices is advantageous in terms of efficiency and operability especially at higher pressures.