After the CCM Medium Pressure Working Group intercomparison indicated that the SMU primary mercury manometer differed by more than 20 ppm from other national standards, attention was paid to determining and eliminating the possible sources of these deviations. These efforts included replacing or redesigning some of the manometer components. The modified manometer design is presented in this paper. A piston gauge has been calibrated in the absolute mode using nitrogen as a pressure media, with the primary standard manometers at four national standards laboratories: Slovensky' Metrologicky' Ustav (SMU), Bratislava; Amt fir Standardisierung, Messwesen und Warenpriifung (ASMW), Berlin; Physikalisch-Technische Bundesanstalt (PTB), Braunschweig; and the National Institute of Standards and Technology (NIST), Gaithersburg; over a period of six years. Each of these manometers is of a different design. This has provided a basis from which to determine how the design changes affect the SMU manometer performance. The results indicate that the previous systematic deviations have been eliminated in the upper pressure ranges. The results for all four manometers agree to within their claimed uncertainties, however at the lowest pressures significant differences still exist and require further investigation.
A comparison between the D. I. Mendeleyev Institute for Metrology (VNIIM, Russian Federation), the Physikalisch-Technische Bundesanstalt (PTB, Germany) and the Slovak Institute of Metrology (SMU, Slovakia) was organized by the VNIIM as the coordinator and pilot laboratory of a COOMET project that started in 1995 and finished in 1998. The comparison was realized on the basis of cross-float experiments with two transfer standards -5 cm 2 piston-cylinder assemblies for pressure balances -manufactured by, and belonging to, the VNIIM. The transfer standards and the methods applied to determine their effective areas, , are described and the comparison results presented. With the equivalence criterion for the agreement between any two participants taken to be ( being the standard uncertainty of the effective area of the transfer standard used), the national standards of the participants for the pressure range covered by the comparison experiments may be considered to be equivalent. As one of the participants in the present comparison (PTB) used the same primary standards in comparisons organized by EUROMET* and by the Consultative Committee for Mass and Related Quantities (CCM), the participants in this COOMET project can indirectly compare their pressure standards with those of other European countries, Japan, and the United States.
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