Realization of a national practical pressure scale for pressures up to 500MPa

The successful realization at the National Physical Laboratory of India of the national practical pressure scale up to 500 MPa is described. A brief a ccount is given of the metrological characterization of the controlled-clea rance piston gauge (CCPG) used as the national primary pressure standard up to 500 MPa. The measured pressure with a definite uncertainty budget has b een used to determine the effective area, Ao, at atmospheric pressure at a reference temperature of 23 degrees C and the pressure distortion coefficie nt, lambda, of the four different piston-cylinder assemblies used as nation al secondary pressure standards. Emphasis is laid on the establishment of t he pyramid structure of the traceability hierarchy according to the Interna tional Organization for Standardization (ISO) and European Go-operation for Accreditation (EA) guidelines for the expression of the uncertainty of mea surement in calibration. The metrological data obtained were found to be wi thin the limits of the uncertainty budgets of international key comparisons and bilateral comparison measurements.