An oscillatory dynamic mode for a watt balance

A watt balance relates mechanical power to electrical power by comparing the gravitational force on a mass with the electromagnetic force on a current-carrying coil in a magnetic field. It is one of the favoured approaches to replacing the present artefact kilogram as it will allow the kilogram to be redefined in terms of the Planck constant. In this paper, we propose an oscillatory approach to the dynamic or moving mode of a watt balance experiment as an alternative to the traditional constant velocity approach. Features of an oscillatory dynamic mode include frequency selection and Fourier analysis to reduce noise due to vibration, the option of larger coil velocities (above 2 mm s −1 ) and smaller coil movement amplitudes (of order ±1 mm) than the constant velocity approach, and direct measurement at the weighing position of the factor γ relating coil current to the gravitational force on the mass. An oscillatory dynamic mode can be used with some of the existing watt balance experiments with the potential to measure γ faster and more precisely than the constant velocity approach.