Edwina Lee Posted November 16, 2018 Posted November 16, 2018 This sounds very dodgy to me, despite it came from BBC Science News 2018-11-16:- https://www.bbc.co.uk/news/science-environment-46143399 The Kibble Balance measures weight in order to deduce the mass of the reference standard weight. Hmmmmm
Strange Posted November 16, 2018 Posted November 16, 2018 It is not quite as simple as that. More here: https://www.nist.gov/si-redefinition/kilogram-kibble-balance The mass is defined in terms of other factors that can all be measured independently of the mass: voltage, current, velocity and g (acceleration). 1
swansont Posted November 16, 2018 Posted November 16, 2018 3 hours ago, Strange said: It is not quite as simple as that. More here: https://www.nist.gov/si-redefinition/kilogram-kibble-balance The mass is defined in terms of other factors that can all be measured independently of the mass: voltage, current, velocity and g (acceleration). It looks like you do a velocity measurement as a calibration, and then the mass determination as a static measurement. With an independent measurement of g. The good thing is that you eliminate the issue of who gets a secondary kilogram standard. Any country can, in principle, realize the standard, though I don't know how they will communicate the information back and forth, like they(we) do with time. But that may be embedded in the calibration info and the new definition of h (and possibly other terms), which would mean that the kilogram will be defined by a certain current, given a certain value of g, and modified by some constant you get from calibration (which accounts for differences in the geometry of the coils and details of the magnets) But I haven't seen any of this kind of detail yet. edit: Nope. Looks like there will still be physical objects, known as "transfer standards"https://www.nist.gov/si-redefinition/kilogram-disseminating-new-kilogram
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