At the National Institute of Standards and Technology a new watt balance, NIST-4, is currently being designed. This apparatus will be used to realize the unit of mass after the redefinition of the SI has taken effect. In order to ensure smooth operation during regularly occurring mass realizations the watt balance should be easy to use and reliable. To meet these requirements we decided to employ a permanent magnet system to generate the magnetic flux. A brief overview of the permanent magnet system as well as the considerations that led to its design is given.
IEEE Transactions on Instrumentation and Measurement
mass, permanent magnet, Planck constant, watt balance, SI units