Investigation of 1 GPa Controlled Clearance Piston Gauge Using Finite Element Analysis

A one GPa controlled clearance piston gauge used as a high pressure standard at KRISS was investigated. In establishing the high pressure standard, the distortion coefficient is one of the most important parameters, but it is not easy to determine. The conventional analysis using a Heydemann-Welch model has a problem when determining a stall pressure, because of the nonlinear characteristic of fall rates with respect to pressure. Some metrological characteristics, such as the distortion coefficient of the piston-cylinder assembly in free deformation (FD) mode and the jacket distortion coefficient and stall pressure in controlled clearance (CC) mode, were investigated using a finite element analysis (FEA). In particular, it was determined that the relation of cubic fall rate to jacket pressure becomes nonlinear above 600 MPa. The FEA results were verified by comparison with a 500 MPa pressure standard and a fall rate measurement of 1 GPa. The most important parameter, the distortion coefficient in the FD and CC mode, was determined to be (7.59 +/- 0.24) x 10(-7) MPa-1 and (3.35 +/- 0.39) x 10(-7) MPa-1, respectively. A zero-distortion coefficient was obtained in the FEA when around 17% of the applied pressure was used as the jacket pressure. This value was similar to the experimentally determined result of around 20%.