This paper describes the facilities, measurement capabilities, and ongoing research activities in the areas of mass and force at the National Institute of Standards and Technology (NIST). The first section of the paper is devoted to mass metrology and starts with a brief historical perspective on the developments that led to the current definition of the kilogram. An overview of mass measurement procedures is given with a brief discussion of current research on alternative materials for mass standards and surface profiles of the U.S. national prototype kilograms. A brief outlook into the future possible redefinition of the unit of mass based on fundamental principles is included. The second part of this paper focuses on the unit of force and describes the realization of the unit, measurement procedures, uncertainty in the realized force, facilities, and current efforts aimed at the realization of small forces.
This paper describes a new approach to link air and vacuum mass measurements using magnetic levitation techniques. This procedure provides direct traceability to national standards, presently defined in ambient air. We describe the basic principles, challenges, initial modelling calculations and performance expectations 1 .
We report a key comparison of 1 kg stainless steel mass standards carried out between February 1995 and October 1997. Organized within the Consultative Committee for Mass and Related Quantities (CCM), the participants included 14 national metrology institutes (NMIs) and the BIPM, with the BIPM serving as pilot laboratory. The 14 NMIs were divided into two groups, each of which determined the mass of two cylindrical travelling standards. In preliminary measurements, the pilot laboratory had determined the important physical properties of the four travelling standards and had monitored their mass stability over time. Measurements within the two groups then proceeded in parallel, with the four travelling standards returning several times to the pilot laboratory in order to monitor their stability. One of the present authors (MG) shows in appendix 3 how to treat comparisons among participants in different 'loops'. As shown in appendix 4, the mass reported by each NMI was derived indirectly from the mass of its national prototype, introducing a significant correction for air buoyancy during this step.The median of all results was taken to be the reference value for this key comparison. The degrees of equivalence are shown in tables 3–5 and summarized graphically in figure 7.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 CCM, according to the
provisions of the Mutual Recognition Arrangement (MRA).
These nominal values have been chosen, because they cover the range of weights mostly used in practice and because a box containing these standards can still be transported by hand-carrying. PTB has accepted the role as pilot laboratory. With the exception of Mexico, the participants are member countries of CCM, in particular:
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