Determination of the Planck constant with the METAS watt balance

The METAS watt balance project was initiated slightly more than a decade ago. Over this time, the apparatus has been through an uninterrupted series of upgrades that have improved its reliability to a point where continuous series of measurements can be taken fully automatically over periods of several months. A comprehensive analysis of possible systematic errors has now been completed and a large set of data has been analysed to calculate a value for the Planck constant h. This paper describes the watt balance in detail, explains the data acquisition and analysis thoroughly and presents the uncertainty budget. The value of the Planck constant determined with our apparatus is h = 6.626 069 1(20)× 10−34 J s with a relative standard uncertainty of 0.29 × 10−6. This value differs from the 2006 CODATA adjustment by 0.024 μW W−1. (Some figures in this article are in colour only in the electronic version)