Abstract
This report summarizes the results of a regional key comparison (APMP-IC-2-97) under the aegis of the Asia Pacific Metrology Program (APMP) for pressure measurements in gas media and in gauge mode from 0.4 MPa to 4.0 MPa. The transfer standard was a pressure-balance with a piston-cylinder assembly with nominal effective area 8.4 mm2 (V-407) and was supplied by the National Metrology Institute of Japan [NMIJ]. Ten standard laboratories from the APMP region with one specially invited laboratory from the EUROMET region, namely Physikalisch-Technische Bundesanstalt (PTB), Germany, participated in this comparison. The comparison started in October 1998 and was completed in May 2001. The pilot laboratory prepared the calibration procedure [1] as per the guidelines of APMP and the International Bureau of Weights and Measures (BIPM) [2–4]. Detailed instructions for performing this key comparison were provided in the calibration protocol [1] and the required data were described in: (1) Annex 3 – characteristics of the laboratory standards, (2) Annex 4 – the effective area (A'p'/mm2) (the prime indicates values based on measured quantities) at 23°C of the travelling standard as a function of nominal pressure (p'/MPa) (five cycles both increasing and decreasing pressures at ten pre-determined pressure points) and (3) Annex 5 – the average effective area at 23°C (A'p'/mm2) obtained for each pressure p'/MPa with all uncertainty statements. The pilot laboratory processed the information and the data provided by the participants for these three annexes, starting with the information about the standards as provided in Annex 3. Based on this information, the participating laboratories are classified into two categories: (I) laboratories that are maintaining primary standards, and (II) laboratories that are maintaining standards loosely classified as secondary standards with a clear traceability as per norm of the BIPM. It is observed that out of these eleven laboratories, six laboratories have primary standards [Category (I)], the remaining five laboratories are placed in Category (II).
The obtained data were compiled and processed under the same program as per the Consultative Committee for Mass and Related Quantities (CCM)/BIPM guidelines. From the data of Category (I), we evaluated the APMP reference value as a function of p'/MPa. Then, we estimated the relative difference of the A'p' values with reference to the APMP reference value for all participating laboratories and we observed that they agree well within their expanded uncertainties. We further estimated the effective area at null pressure and at 23°C (A'0/mm2) and the pressure distortion coefficient (λ'/MPa-1) of the transfer standard for all the participating laboratories. We then estimated the relative deviation of the A'0/mm2 from the reference value for all eleven laboratories and compared this with their estimated expanded uncertainties. The result is once again extremely encouraging and all these eleven laboratories are agreeing within their estimated maximum expanded uncertainties. We also estimated the degree of equivalence between any two participating laboratories following a matrix mechanism. This once again agrees extremely well within the estimated relative standard uncertainty, which is derived for the two participating laboratories. Finally, a new method has been introduced to evaluate these results and establish a link to CCM.P-K1c and EUROMET.M.P-K2 at two nominal pressures, near 1 MPa and 4 MPa. Again the results show an agreement of all participating laboratories in the present comparison to within the estimated expanded uncertainties using a coverage factor k = 2.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the APMP, according to the provisions of the Mutual Recognition Arrangement (MRA).