Calculation of the Distortion Coefficient and Associated Uncertainty of a PTB 1 GPa Pressure Balance Using Finite Element Analysis -EUROMET Project 463

摘要

The pressure distortion coefficients and their uncertainties of a PTB piston-cylinder assembly used in a pressure balance for the realisation of the pressure unit up to 1 GPa are determined by the finite element methods of the national metrology institutes and their partners participating in EUROMET project 463. On the basis of the experimental data including the elastic properties of the piston-cylinder materials, the pressure-dependent density and viscosity of the pressure-transmitting fluid, dimensions of the piston, cylinder and the piston-cylinder clearance as well as the conditions on the piston-cylinder boundaries, axisymmetric models are developed and analysed. The methods of the participants are described and the results such as pressure distributions and radial distortions along the piston-cylinder engagement length, pressure distortion coefficients and the piston fall rates in dependence on pressure are presented for the free-deformation and the controlled-clearance operation modes of the assembly. The uncertainty budgets are developed and analysed. The theoretical results are verified by comparing them with the distortion coefficients determined by an experimental method and with the jacket pressure distortion coefficients.