Calculation of the distortion coefficient and associated uncertainty of PTB and LNE 1 GPa pressure balances using finite element analysis—EUROMET project 463

Results for pressure distortion coefficients (λ) obtained by five national metrology institutes with finite element methods (FEM) for PTB and LNE 1 GPa piston–cylinder units are presented. For the PTB unit they demonstrate good agreement of the FEM and the experimental distortion coefficients but rather large differences in the uncertainties, pressure distributions, gap profiles and piston fall rates. The reasons for differences between the theoretical real-gap and experimental λ obtained for the LNE unit require further clarification. The uncertainty of the gap geometry is identified as the main uncertainty source.