Since 2005 the BIPM has been developing a Kibble balance as a means for the practical realization of the expected new definition of the kilogram in terms of the Planck constant. The BIPM Kibble balance operates using a 0.5 T radial magnetic field, a 250 mm diameter and 1100 turn induction coil, a flowing current of ±13 mA and a test mass of 1 kg. Coil velocity is about 1 mm s1 with typical excursion of 20 mm.
The apparatus is fully operational in air and in vacuum. The relative type B uncertainty on the Planck constant determination is currently about 2 x 107. The type B uncertainty is dominated by the residual misalignment of the interferometer laser beam due to the limited mechanical stability of the interferometer mount. A novel interferometer mounted on a much more stable support is being designed with the objective to reduce the uncertainty within 1 x 107. The standard deviation on the mean value for one week of measurements is a few parts in 108.
For further details see:
- H. Fang, F. Bielsa, A. Kiss, T. Lavergne, Y. F. Lu, L. Robertsson, E. de Mirandés, S. Solve and M. Stock, Progress on the BIPM watt balance, Proc. CPEM 2016, 2016.
- H. Fang, F. Bielsa, S. Li, A. Kiss, and M. Stock, The BIPM Kibble Balance for the realization of the redefined kilogram, Proc. CPEM 2018, 2018.