Search

For the accurate measurement of small masses and forces in a traceable manner to the new definition of the kilogram, a voltage balance apparatus that uses electrostatic force between coaxial electrodes has been developed at the National Metrology Institute of Japan (NMIJ). In the voltage balance measurements, the coaxial electrodes of the apparatus are mechanically aligned by measuring the capacitance to achieve accurate small mass measurements. In this work, we investigated the effect of surface roughness on mechanical alignment of coaxial electrodes for voltage balance measurements using the finite element method (FEM). The results indicate that misalignments caused by surface roughness alter the capacitance gradient but do not significantly increase unwanted lateral forces in the mass measurement compared to that in the ideal condition.

The new definition of the kilogram was implemented on May 20, 2019. The kilogram is presently defined by the Planck constant. On the basis of the new definition, the kilogram will be realized at the National Metrology Institute of Japan by the X-ray crystal density method using 28Si-enriched spheres. For the realization, the volume of 28Si-enriched spheres is measured by optical interferometry. The sphere surface is also characterized by X-ray photoelectron spectroscopy and ellipsometry. The relative standard uncertainty of the realization is estimated to be 2.1 × 10−8. This corresponds to the realization of the new kilogram with a standard uncertainty of 21 μg for 1 kg. Details of the realization and future dissemination of mass standards in Japan based on the 28Si-enriched spheres are described.