We report the results of a bilateral comparison of pressure measurement between NIST and NPLI using a piston gauge transfer standard (TS), designated as NPLI-4, over the range of nominal applied pressure 0.4 MPa to 4.0 MPa. This TS was cross-floated against the laboratory secondary standard designated as PG13 at NIST, USA and against NPLI-8 at NPLI, India. The nominal pressure points of the bilateral comparison were (0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2, 3.6 and 4.0) MPa, respectively. The comparison was performed in both the institutes in identical pressure cycles in increasing pressures. The comparison data were analyzed in terms of the effective area [Ap (mm2)] as a function pressure [p (MPa)] of the TS at the above-mentioned pressures. We have also estimated the zero pressure effective area [A0 (mm2)] and the pressure distortion coefficient [l (MPa-1)] of the transfer standard. The consistency of the results at every pressure in the range indicates that the laboratory standards used in this comparison are compatible, uniform and can be considered traceable to each other. Finally, the degree of equivalence between NPLI and NIST is 11.4x10-6 or better, which is always less than the relative standard uncertainty of the difference (33.6x10-6).
Pub Type: Journals
bilateral comparison, key comparison, piston cylinder assembly, pressure metrology, pressure standard