Magnet system for the Planck-balance
The current definition of the unit kilogram by an artifact is about to be replaced by a definition based on a fundamental constant, which is the Planck constant. To establish the link between a mass standard and the Planck constant an instrument called Watt- or Kibble-Balance can be used. This instrument uses a virtual equilibrium between mechanical and electrical power to connect the mass to the electrical quantities which can be defined from the Planck constant using the Josephson- and the Quantum-Hall effect. After the redefinition of the unit, the new definition can be realized not only for masses of 1 kg but for any arbitrary mass value. Consequently the new definition can be directly applied to weighing processes in industry if a suitable measurement system exists. In this paper we briefly describe the design of such a weighing system, called the Planckbalance PB2 which is designed to realize the new definition in a mass range from 1 mg to 100 g. In accordance to our theoretical estimations we aim for achieving uncertainties comparable to current mass disseminations using calibrated weights of class E2. The magnet system is a crucial part of the PB2, since it is responsible for compensation of the weight of up to 100 g with a minimal amount of power loss and because it needs to be characterized with relative uncertainties in the sub ppm range. This article is dedicated to the design considerations for the magnet system which were done using an analytical and a numerical approach. The results are compared to initially obtained measurement data of a prototype setup.
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