An Introduction to Mass Metrology in Vacuum

Illustration of vacuum to air transfer of kilogram calibration using magnetic levitation. A standard mass in the vacuum chamber is compared to a mass in the air chamber using the same mass balance.
Illustration of vacuum to air transfer of kilogram calibration using magnetic levitation. A standard mass in the vacuum chamber is compared to a mass in the air chamber using the same mass balance.

By Patrick J. Abbott & Zeina J. Jabbour

Mass metrology carried out in atmospheric pressure air is suitable for most every critical application. However, mass metrology in vacuum is important in several current research projects. Performing mass measurements in a vacuum environment eliminates the need for air buoyancy corrections and hence allows a more precise determination of true mass. In addition, the major experiments for redefining the kilogram in terms of a physical constant of nature, the watt balance and the Avogadro project, both operate in vacuum. A kilogram that is redefined by these experiments will require making the transfer from mass in vacuum to mass in air. Therefore, understanding mass metrology in a vacuum environment is essential for doing the research necessary to maintain world-class mass standards. In this paper, we present an introduction to the techniques and apparatus needed for vacuum mass metrology and discuss some of the work in this area being done at NIST.


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