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No.27
November 2003
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Final report of APMP Key Comparison
(APMP.M.P-K1c)
[Results of the
APMP Pressure key comparison in gas media and gauge mode from
0.4 to 4.0 Mpa]
Dr.
A.K. Bandyopadhyay (
akband@mail.nplindia.ernet.in )
Pressure
and Vacuum Standards, National Physical Laboratories
This report summarizes the
results of a regional key comparison (APMP-IC-2-97) under the
aegis of Asia Pacific Metrology Program (APMP) for pressure measurements
in gas media and in gauge mode from 0.4 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
had started from October, 1998 and was completed in May, 2001.
The pilot laboratory prepared the calibration procedure as per
the guidelines of APMP and International Bureau of Weights and
Measures (BIPM) [2-4]. Detailed instructions for performing this
key comparison were provided in the calibration protocol and the
required data were described in : (1) Annex 3 - characteristics
of the laboratory standards, (2) Annex 4 - the effective area
(AÕpÕ /mm2) at 23oC of the traveling standard as a function of
nominal pressure (pÕ/MPa) (five cycles both increasing and decreasing
pressures at ten pre-determined pressure points) and (3) Annex
5 - the average effective area at 23oC (AÕpÕ/mm2 ) obtained for
each pressure pÕ / 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 have evaluated the
APMP reference value as a function of pÕ/MPa. which is shown in
Figure 1.
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Then, we have estimated
the relative difference of A'pÕ value with reference to APMP reference
value for all participating laboratories and we observed that
they agree well within their expanded uncertainty statement [
shown in Fig.2]. We have also determined the degree of equivalence
between any two participating laboratories following the matrix
mechanism. This is once again agreeing extremely well within the
estimated relative standard uncertainty, which is derived for
these 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.
Following the rules of BIPM, after the formal approval
of this report by the President, CCM, it is now proposed to be
included in the Appendix B of the BIPM key comparison database
(KCDB) in September, 2003. |
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