Estimation of the effective area of the controlled-clearance pressure balance for pressures up to 500 MPa

We are now developing a new controlled-clearance (CC) pressure balance with the aim of improving the hydraulic pressure standard. The effective areas of the three kinds of CC piston-cylinders, whose maximum pressures are 100 MPa, 200 MPa, and 500 MPa, were estimated based on the Ileydemann-Welch model. To estimate the pressure dependence of the effective area, two characterization experiments, fall-rate and cross-float measurements, were performed. In this paper, the procedures for the characterization experiments are explained in detail. Then, results of the experiments for the 100 MPa CC piston-cylinder are presented. To verify our estimation of the effective area based on the Heydemann-Welch model, piston-cylinders were calibrated against the evaluated CC piston-cylinders and against our current pressure scale separately. Then, two results were compared in terms of the pressure distortion coefficient. For all pressure ranges, two results were in good agreement with each other. It is found that the estimation of the pressure dependence of the effective area is consistent with our current pressure scale.