Measurements made with watt balances are paving the way to a new definition of the kilogram based upon a fixed value of the Planck constant. The Bureau International des Poids et Measures (BIPM) are developing a simultaneous moving and weighing variant of the watt balance technique, which requires a superconducting coil to reach its ultimate uncertainty. The BIPM technique has the advantage that it eliminates the requirement for extreme stability in the magnetic field employed by conventional watt balances, but requires cryogenic operation of parts of the balance to achieve a low uncertainty. This paper proposes a simple method, by which the BIPM technique can be made to operate at room temperature with no loss of accuracy. The superconducting coil is replaced by a bifilar coil and the measurement procedure is modified to eliminate any inequality between the two conductors in the bifilar coil. The new technique is not subject to the many secondary sources of uncertainty arising from cryogenic operation.
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