An experimental procedure has been developed to accurately align the magnetic field of the circuit perpendicular to the direction defined by the local acceleration of gravity. The technique is based on a rotating Hall probe and a high-sensitive tiltmeter.
The magnetic plane at the central position inside the gap was aligned to better than 10 μrad with an uncertainty below 30 µrad. Constancy of the magnetic plane inclination was verified at the 30 µrad level over a length of 40 mm in the vertical direction. The geometry of the magnetic circuit was also characterized, confirming the suitability of the magnetic circuit for use in the BIPM watt balance at the 108 uncertainty level.
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|Experimental set-up used for aligning the magnetic field.|