Bureau International des Poids et Mesures (BIPM), Pavillon de Breteuil, 92312 Sèvres CEDEX, France.
Philos Trans A Math Phys Eng Sci. 2011 Oct 28;369(1953):3936-53. doi: 10.1098/rsta.2011.0184.
Since 1889, the international prototype of the kilogram has served as the definition of the unit of mass in the International System of Units (SI). It is the last material artefact to define a base unit of the SI, and it influences several other base units. This situation is no longer acceptable in a time of ever-increasing measurement precision. It is therefore planned to redefine the unit of mass by fixing the numerical value of the Planck constant. At the same time three other base units, the ampere, the kelvin and the mole, will be redefined. As a first step, the kilogram redefinition requires a highly accurate determination of the Planck constant in the present SI system, with a relative uncertainty of the order of 1 part in 10(8). The most promising experiment for this purpose, and for the future realization of the kilogram, is the watt balance. It compares mechanical and electrical power and makes use of two macroscopic quantum effects, thus creating a relationship between a macroscopic mass and the Planck constant. In this paper, the operating principle of watt balance experiments is explained and the existing experiments are reviewed. An overview is given of all available experimental determinations of the Planck constant, and it is shown that further investigation is needed before the redefinition of the kilogram can take place. Independent of this requirement, a consensus has been reached on the form that future definitions of the SI base units will take.
自 1889 年以来，国际千克原器一直作为国际单位制（SI）中质量单位的定义。它是最后一个定义 SI 基本单位的物质人工制品，并且还影响着其他几个基本单位。在测量精度不断提高的时代，这种情况已经不再可以接受。因此，计划通过固定普朗克常数的数值来重新定义质量单位。同时，其他三个基本单位，安培、开尔文和摩尔，也将重新定义。作为第一步，千克重新定义需要在当前 SI 系统中非常精确地确定普朗克常数，其相对不确定度约为 1 比 10(8)。为此目的最有前途的实验，也是未来实现千克的实验，是瓦特天平。它比较机械和电力，并利用两个宏观量子效应，从而在宏观质量和普朗克常数之间建立了关系。本文解释了瓦特天平实验的工作原理，并回顾了现有的实验。概述了所有可用的普朗克常数实验测定，并表明在重新定义千克之前还需要进一步研究。独立于这一要求，已经就 SI 基本单位的未来定义形式达成共识。
