New measurement useful for "redefinition of kilogram" announced by National Institute of Standards and Technology

International unit systemKilogram (kg), which is the basic unit of mass of SI,International Weight BureauIt is based on "international kilogram prototype" which is a 1 kg metal mass made of platinum (platinum) and iridium alloy stored at However, the kilogram prototype is regarded as the only unstable unit in the international unit system because mass will fluctuate even if it is stored strictly, and "kilogram redefinition" based on more general physical quantity Where is being debated for a long time. Toward redefinition of kilogramNational Institute of Standards and Technology(NIST)Planck's constantAlthough I have listed the measurement method of kilogram based on NIST, the measurement method with high accuracy of uncertainty of 1 / 1,300,000 was announced in the paper newly released by NIST.

New Measurement Will Help Redefine International Unit of Mass | NIST
https://www.nist.gov/news-events/news/2017/06/new-measurement-will-help-redefine-international-unit-mass


Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017
(PDF file)http://iopscience.iop.org/article/10.1088/1681-7575/aa7bf2/pdf

The National Institute of Standards and Technology (NIST) has succeeded in measuring the most accurate kilogram so far by using the state-of-the-art equipment kibble balance, making the definition of international kilogram a new definition based on Planck's constant We are proposing. Kibble balance and "Watt balance"It refers to an electric balance that can measure weight with high precision using current and voltage. It is a balance to measure the weight of an object, but by measuring the current that can support the standard kilogram mass, it is possible to use it opposite to its original way, that it can accurately determine 1 kg of mass. It is said that current and voltage units can be defined by using physical constants such as Planck's constant, and more precise definitions can be measured than the definition using international kilogram prototype.


Measurement based on Planck's constant also in NIST in 2016And announced that the uncertainty of the measurement was 34 billionths. This time it seems that we made it possible to measure with uncertainty of 13 billionths.

The data necessary for the redefinition of the international unit system had to be published as a paper by July 1, 2017, but NIST compiled the results of this measurement with the international scientific journal Metrologia 6 It is published on the 30th of the month and it will be discussed whether it is suitable as a new definition of kilogram at the international conference to be held in 2018.