Intercomparison of Nine National High-vacuum Standards under the Auspices of the Bureau International des Poids et Mesures

Abstract

The Bureau International des Poids et Mesures has initiated world-wide intercomparisons of pressure standards. The intercomparison in the regime of very low pressures, i.e. 10-4 to 1 Pa, using Ar as the test gas, has now been completed with the participation of laboratories in nine countries (in alphabetical order): Czechoslovakia, Federal Republic of Germany, France, India, Italy, Japan, People's Republic of China, UK and United States of America. In addition, five of these laboratories made measurements using H2 as the test gas. Four spinning-rotor gauges were employed as transfer standards. The achieved transfer uncertainty between the pilot laboratory (Physikalisch-Technische Bundesanstalt) and a participating laboratory lies between 0.16% and 0.30% (1σ) for Ar and has allowed an intercomparison at this level of accuracy. At all investigated pressures the standards in the various laboratories lie within an interval of ±3% around the standard of the pilot laboratory. For a brief synopsis of the intercomparison results, the calibration data of each laboratory for one gas species are reduced to a single number, i.e., the average over the pressure range 10-3 to 1 Pa, although this procedure is somewhat arbitrary and obscures scatter and pressure-dependence of some calibration results. These averages deviate from their mean by not more than about 1%. Systematic deviations between some laboratories are clearly identifiable: however, for most of the laboratories it appears that these are compatible with the estimated uncertainties of the pressure generation and the transfer uncertainty.

Results of a bilateral comparison of the high-vacuum primary standards at the Korea Research Institute of Standards and Science and the UK National Physical Laboratory

“…The comparison was hampered to some degree by instabilities in the transfer standards, which exceeded the uncertainties associated with the primary standards. From Table 1, a change in of up to 1.2 % between the two sets of measurements at the KRISS is apparent for gauge L while a smaller change of up to 1 % was exhibited for gauge M. These changes, which possibly occurred as a result of the transportation of the gauges, confirm the difficulties in carrying out comparisons in this pressure region [4][5][6].…”

NIST Calibration Services for Spinning Rotor Gauge Calibrations

“… Participating in international comparisons. Four comparisons [34,35,36,37] have been completed since the publication of the previous SP-250-34 [2]. In addition, NIST participated in an SRG key comparison, the CCM.P-K14, during 2010.…”

High-accuracy calibration in the vacuum range 0.3 Pa to 4000 Pa using the primary standard of static gas expansion

“…The amount of gas transferred can be calculated from the pressures (at thermal equilibrium) before and after expansion. In thermodynamics, the relation between temperature and pressure is given by Poisson's equation [17]: (9) where is the isentropic coef cient of the gas species.…”

“…Furthermore, this method is the most accurate primary standard at pressures below 1 Pa. Various metrological institutions have operated static gas expansion systems successfully for several years, such as the Physikalisch-Technische Bundesanstalt (PTB, Berlin, Germany), the National Physical Laboratory (NPL, Teddington, UK) and the IMGC [9].…”