Design of the Permanent-Magnet System for NIST-4

A new watt balance, i.e., NIST-4, is currently being designed at the National Institute of Standards and Technology. This apparatus will be used to realize the unit of mass after the redefinition of the kilogram has taken effect. In order to ensure smooth operation at regular mass realizations, the watt balance should be easy to use and reliable. To meet these requirements, a permanent-magnet system will be implemented to generate the magnetic flux required to operate NIST-4. A brief overview of the permanent-magnet system and its design considerations are given.