First measurements of the flux integral with the NIST-4 watt balance

摘要

In early 2014, construction of a new watt balance, named NIST-4, has startedat the National Institute of Standards and Technology (NIST). In a wattbalance, the gravitational force of an unknown mass is compensated by anelectromagnetic force produced by a coil in a magnet system. Theelectromagnetic force depends on the current in the coil and the magnetic fluxintegral. Most watt balances feature an additional calibration mode, referredto as velocity mode, which allows one to measure the magnetic flux integral tohigh precision. In this article we describe first measurements of the fluxintegral in the new watt balance. We introduce measurement and data analysistechniques to assess the quality of the measurements and the adverse effects ofvibrations on the instrument.