Establishing traceability from the Kibble balance

In 2019, the kilogram was redefined from the international prototype in Paris to Planck’s constant. In practice, the kilogram is realized according to the new definition using a Kibble balance, in which a magnetic force is balanced against the gravitational force arising from the test mass. The national metrology institutes for mass and for electrical quantities are collaborating with the National Physical Laboratory (NPL, United Kingdom) to develop a next‑generation Kibble balance to realize the kilogram. Since the principle relies on force equilibrium, it is necessary to know the gravitational acceleration very precisely in order to determine the mass.

This project aims to establish traceability from the force realization provided by the Kibble balance currently being developed by NPL and RISE. The focus is on the mathematical modelling required for this traceability and on how measurement uncertainty propagates through these models. This includes precise modelling of gravity in the Kibble laboratory for the conversion from force to mass, as well as the development of a new comparison scheme to establish traceability from the mass in the Kibble balance to the other mass standards used by the national metrology institute for mass in its calibration activities.