Status of the BIPM Watt Balance

Abstract

This paper presents the progress made to improve and develop the Bureau International des Poids et Mesures (BIPM) watt balance during the last two years. A reduction by a factor of five of the type A uncertainty was achieved by refining the velocity measurement. The BIPM simultaneous weighing and moving approach was experimentally compared to a bifilar coil technique. The relative difference to the Planck constant determination between the two approaches is 2 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> with a type A uncertainty of 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> . A vacuum enclosure located in a dedicated laboratory with better thermal and vibrational isolation is ready to receive the present apparatus for further improvement.