Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology

摘要

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value h = 6.62606979(30) × 10~(-34) Js. The relative standard uncertainty is 45 × 10~(-9). This result is 141 × 10~(-9) fractionally higher than h_(90). Here h_(90) is the conventional value of the Planck constant given by h_(90) = 4/(K_(J-90)~2R_(K-90)), where K_(J-90) and R_(K-90) denote the conventional values of the Josephson and von Klitzing constants, respectively.