The BIPM Kibble Balance: improvements and measurements

This paper summarizes the various improvements to and measurements carried out with the BIPM Kibble balance for realizing the definition of the mass unit in terms of the Planck constant. Measurement uncertainty has been significantly reduced by a factor of four. Mass measurement of a 1 kg Pt/Ir artefact was carried out during three periods in 2019. The mass of the artefact was measured in vacuum with a standard uncertainty of about 50 μg. Efforts are underway to further reduce measurement uncertainty which is dominated by the misalignment and the electrical measurements.