Displacement Measurements in UME Oscillating-Magnet Kibble Balance

摘要

The redefinition of kilogram in terms of Planck constant rather than a physical artifact of International Prototype of Kilogram will be put into force in May 20th, 2019. National Metrology Institute of Turkey contributes to the ongoing worldwide scientific work on the realization of kilogram with an Oscillating-Magnet Kibble Balance experiment. The novel dynamical measurement procedure developed for Kibble Balance Experiment in Turkey poses the advantage of being less sensitive to the environmental disturbances. Precise displacement measurements between the coil suspended from a balance and the surrounding magnetic circuit are vital to reach the required uncertainties in the realization experiments via Kibble balance. The Michelson Interferometer and the Fabry-Perot Interferometer are commonly used in precise displacement measurements in worldwide Kibble balances. A commercial, miniature, plane mirror Michelson Interferometer with compact sensor head is used in the Kibble Balance Experiment of Turkey. In this paper, we determine the contribution of ultra-small oscillations to Planck constant by taking simultaneous displacement measurements on two back-to-back mirrors attached to the piezoelectric transducer undergoing an oscillatory motion with Michelson Interferometer and Fabry-Perot Interferometer. Although, in the specification of these instruments it has been stated that extreme precautions are required in the environmental conditions to be able to measure displacements with ultra-small amplitudes, following the novel measurement procedure makes such measurements possible in a regular laboratory environment which allows us to investigate the resolution performance of these instruments in laboratory conditions. Consistent results with resolution uncertainties of 1.4 × 10~(-9) and 2.2 × 10~(-9) are obtained for Michelson Interferometer and the Fabry-Perot Interferometer, respectively. As the expected relative uncertainty in the redefinition experiments of the kilogram is above the resolution uncertainties of both interferometers, we may conclude that a commercial, miniature, plane mirror Michelson Interferometer with compact sensor head will serve for our purposes in the route for the redefinition of kilogram.