Expérience française de balance du watt : conception d’un fléau de balance monobloc et étude de son comportement mécanique

Abstract

Abstract. Since 2005, the French watt balance experiment, installed at the LNE, has been using a balance beam with removable flexure hinges designed at the CNAM. With this balance, a first determination of the Planck constant in air was performed in 2014. This balance beam presents some drawbacks. First, it is difficult to mount and adjust the hinges. Secondly, the use of clamped flexure strips used as pivots limits the beam sensitivity and measurement repeatability, moreover the central flexure strip twists under the effect of unwanted horizontal forces at the ends of the beam, which leads to a potential measurement error. For these reasons, a new, single-piece balance beam has been designed. It is not only easier to mount and adjust than its predecessor, but also free of unwanted stresses such as shear force on the hinges. This ensures that, once the beam is loaded, the rotation axes are by construction parallel and coplanar. In addition, the use of a double central hinge strongly reduces the torsion effect.

B7.3 - Beam Horizontality Determination in the LNE Kibble Balance Experiment

“…The LNE Kibble balance beam is a single-piece symmetrical 100 mm length arms with three double flexure pivots [4], [5] . Under charge, these three centers of rotation are aligned by design and therefore define the segment which is supposed to be aligned with the horizontal during a static phase.…”