We report here the results of a bilateral comparison of pressure measurement between the National Institute of Standards and Technology (NIST), Gaithersburg, USA and the National Physical Laboratory (NPLI), New Delhi, India, over the range of nominal applied pressure 40 MPa to 200 MPa at a reference temperature of 23 oC. The comparison used two transfer standards (TS), designated as NPLI-100MPN (pressure range 10 MPa to 100 MPa with nominal effective area 9.80 mm2) and NPLI-500MPN (pressure range 50 MPa to 500 MPa with nominal effective area 1.96 mm2). These two TSs were cross-floated against the laboratory standards of NPLI and NIST at nominal pressure points of (40, 60, 80, 80, 60, 40) MPa for NPLI-100MPN and (80, 100, 120, 140, 160, 180, 200, 200, 180, 160, 140, 120, 100, 80) MPa for NPLI-500MPN, respectively. The NPLI laboratory standard was NPLI-200MPN with nominal effective area 4.90 mm2, and the NIST laboratory standard was PG21 with nominal effective area 8.40 mm2. Testing occurred at NIST during July to August, 2003, and testing occurred at NPLI during January to February, 2004. The comparison was performed in both the institutes in three complete and identical pressure cycles in increasing and decreasing pressures using both TSs. The comparison data were analyzed in terms of the effective area [Ap (mm2)] as a function of pressure [p (MPa)] of the two transfer standards in the respective pressure ranges of (40 to 80) MPa and (80 to 200) MPa. The degree of equivalence between NPLI and NIST is given as the relative difference in the institutes results for effective area of the transfer standards, and is within 7.7x10-6 in the whole pressure range (40 to 200) MPa. This is substantial smaller than the standard uncertainty in the difference in effective area, which is estimated as 44x10-6.
Pub Type: Journals
bilateral comparison, key comparison, piston cylinder assembly, pressure metrology, pressure standard, transfer standard