The NIST-4 Kibble balance, which began full operation in early 2015, measured the Planck constant to within 13 parts per billion in 2017, which was accurate enough to assist with the 2019 redefinition of the kilogram.
A Kibble balance is an electromechanical measuring instrument that measures the weight of a test object very precisely by the electric current and voltage needed to produce a compensating force. It is a metrological instrument that can realize the definition of the kilogram unit of mass based on fundamental constants.[1][2]
It was originally called the watt balance because the weight of the test mass is proportional to the product of current and voltage, which is measured in watts. In June 2016, two months after the death of its inventor, Bryan Kibble, metrologists of the Consultative Committee for Units of the International Committee for Weights and Measures agreed to rename the device in his honor.[3][4]
Prior to 2019, the definition of the kilogram was based on a physical object known as the International Prototype of the Kilogram (IPK).
After considering alternatives, in 2013 the General Conference on Weights and Measures (CGPM) agreed on accuracy criteria for replacing this definition with one based on the use of a Kibble balance. After these criteria had been achieved, the CGPM voted unanimously on November 16, 2018, to change the definition of the kilogram and several other units, effective May 20, 2019, to coincide with World Metrology Day.[3][5][6][7][8] There is also a method called the joule balance. All methods that use the fixed numerical value of the Planck constant are sometimes called the Planck balance.
^Robinson, Ian A.; Schlamminger, Stephan (2016). "The watt or Kibble balance: A technique for implementing the new SI definition of the unit of mass". Metrologia. 53 (5): A46–A74. Bibcode:2016Metro..53A..46R. doi:10.1088/0026-1394/53/5/A46. PMC 8752041. PMID 35023879.
^
Palmer, Jason (2011-01-26). "Curbing the kilogram's weight-loss programme". BBC News. BBC News. Retrieved 2011-02-16.
^ ab
"The Kibble Balance". Education. UK National Physical Laboratory website. 2016. Retrieved 15 May 2017.
^Consultative Committee for Units (CCU),
Report of the 22nd meeting (15-16 June 2016), pp. 32-32, 35
^Cho, Adrian (2017). "Plot to redefine the kilogram nears climax". Science. 356 (6339): 670–671. doi:10.1126/science.356.6339.670. PMID 28522473.
^Milton, Martin (14 November 2016). "Highlights in the work of the BIPM in 2016" (PDF). p. 10. Archived from the original (PDF) on 1 September 2017. Retrieved 1 September 2017.
^Decision CIPM/105-13 (October 2016)
^Materese, Robin (2018-11-16). "Historic Vote Ties Kilogram and Other Units to Natural Constants". NIST. Retrieved 2018-11-16.
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