Calculation of Effective Area and Uncertainty for a Dimensionally Characterized 50 mm Piston-Cylinder Used as a Primary Reference for Pressure

摘要

Dimensional measurements of piston-cylinders for the purpose of defining effective area have improved to a level that allows laboratories to use them as primary references for pressure. Because of their relatively large size and uniform cylindrical geometry, DHI's 50 mm tungsten carbide piston-cylinders are frequently utilized as primary standards in pressure based on a dimensionally characterized effective area. Because of the very low uncertainties in diameter, roundness and straightness measurements, it is essential to properly model the piston-cylinder annular space based on those dimensional measurements. This paper describes a model for calculating the effective area from dimensional measurements and also provides a method for calculating the uncertainty in the resultant effective area and final uncertainty in pressure.