Precisely measuring the Planck constant by electromechanical balances

CODATA Recommended Values of the Fundamental Physical Constants: 2010

“…We consider here and in the following section the two new watt-balance measurements of K 2 J R K = 4/h. For reviews of such experiments, see, for example, the papers of Eichenberger et al (2009); Li et al (2012); Stock (2011). The basic idea is to compare electrical power measured in terms of the Josephson and quantum Hall effects to the equivalent mechanical power measured in the SI unit W = m 2 kg s −3 .…”

30Si Mole Fraction of a Silicon Material Highly Enriched in 28Si Determined by Instrumental Neutron Activation Analysis

“…In this framework, there is an ongoing attempt to redefine the kilogram in terms of an exact, fixed value of the Planck constant, h. 2−4 At present, there are two independent techniques capable to determine h to within the required accuracy. The first is based on the watt balance (WB) method 5,6 and the latter is based on the X-ray crystal density (XRCD) method. 7,8 The WB approach determines h by measuring the electromagnetic force necessary to support 1 kg mass whereas the XRCD approach determines h by measuring the Avogadro constant, N A , which is linked to h through the accurately known molar Planck constant, N A h.…”

Progress on accurate measurement of the Planck constant: Watt balance and counting atoms

“…Therefore, improving the measurement accuracy of the Planck constant can synchronously reduce the uncertainties of these related constants. [21] Accurate measurement of the Planck constant was selected as one of the most difficult scientific problems in the worldwide research in 2012, [22] since any of such approaches should combine the most precise techniques in electrical, mechanical, optical, and chemical metrology. A lot of early approaches were tried in history, e.g., the ampere balance, [23] the voltage balance, [24] the Faraday constant method, [25] etc.…”