Uncertainty estimation of the pressure generated by the controlled-clearance pressure balance in NMIJ

A new pressure balance with a controlled-clearance (CC) piston-cylinder has been developed with the aim of reducing the uncertainty of the pressure especially at high pressure. The effective area of the CC piston-cylinder was estimated based on the Heydemann-Welch model. Two parameters in this model, the jacket pressure coefficient and the zero clearance jacket pressure, were determined from characterization experiments. Then, the pressure dependence of the effective area and its uncertainty were calculated. In this paper, the uncertainty of the effective area for a 100 MPa piston-cylinder is evaluated in detail. The resultant uncertainty of the pressure dependence of the effective area was found to be less than 0.7 times 10^-7 MPa^-1 at pressures higher than 20 MPa.