The BIPM Kibble balance

The BIPM Kibble balance operates with the following parameters: a radial magnetic field of 0.5 T, an induction coil of 1060 turns of diameter 250 mm, a coil current of ±13 mA and a mass standard of 1 kg. The coil travels over 15 mm at a velocity of about 1 mm s^–1. The mechanical system, the magnet, the mass loading and exchanger system as well as the optical system are housed in a vacuum enclosure and the experiment is run under vacuum at approximately 0.03 Pa. The experiment is housed on a large concrete block in a closed cabinet inside a laboratory with an air-conditioning system.

The main distinctive feature of the BIPM Kibble balance is its implementation of a one-mode measurement scheme, in addition to the conventional two-mode approach. In the one-mode scheme, a current flows through one of the windings of a bifilar coil in both weighing and moving measurements. The scheme hence makes the experiment less sensitive to changes in the magnetic field which varies with the coil current and alignment as compared to a one-mode Kibble balance. In addition, a comparison of measurements carried out using the two schemes may provide a better understanding of the limiting factors and possibly reveal some unexpected effects unique to each technique.

Selected publications

Note: The international metrology community renamed their moving-coil watt balances as Kibble balances in honour of the pioneering work in this field by Dr Bryan Kibble, who passed away in 2016.