On the determination of a piston prover dead volume

Dead volume in a piston prover is the part of the internal volume which is never occupied by the piston. It obviously affects measurements performed through the prover, the specific effect depending on the data analysis procedure. In INRIM test rigs, which apply the mass balance method (difference between the estimates of the gas mass at the beginning and at the end of the measurement), the evaluation of the corrections requires knowledge of the initial measurement volume, which depends on the dead volume. Currently, INRIM evaluates the dead volume by geometrical analysis, which involves a large uncertainty. We will propose a method for the dead volume evaluation based on the addition of a well-defined quantity of gas (measured by integration of the output of a calibrated MFC) and by measuring the variation of thermodynamic conditions within the piston. The uncertainty budget of the measurement will be analysed in full detail.