Elastic distortion calculations at PTB on a PTB 400 MPa pressure balance as part of EUROMET project 256

The elastic distortion of piston-cylinder units used for the measurement of pressure leads to a change of their effective areas and must be taken into account to calculate the latter with satisfactory accuracy. In this work, which is part of EUROMET Project 256, the elastic distortions of a unit applied at the PTB in a primary standard pressure balance for the pressure range up to 400 MPa are calculated using Finite Element Analysis (FEA). The radial displacements of the jacket surfaces of the piston and cylinder bore and the pressure distribution in the clearance between them are calculated iteratively to derive the pressure distortion coefficient of the unit. Calculations made under different boundary conditions to study the influence of pressure-balance assembly elements in contact with the piston and the cylinder on their elastic distortions prove the unit to be of the free deformation type. The dependence on pressure of the fall rate of the piston in the cylinder was measured experimentally and calculated theoretically using different models. Elastic distortions of piston and the cylinder, pressure distributions and pressure distortion coefficients that are computed in this work using FEA and the simplified theory and were obtained for this piston-cylinder unit by other participants of EUROMET Project 256 are in agreement. It has been ascertained that deviations of the piston shape and the cylinder bore shape from a strictly cylindrical one have a greater influence on the effective area than the application of different calculation methods assuming a model of an exactly cylindrical piston and cylinder. (orig.)SIGLEAvailable from TIB Hannover: RN 2495(60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman