Experimental verification of coil motion misalignment insensitivity in a Kibble balance

PTB's redesigned Planck-Balance – a compact variant of a Kibble balance – is used to investigate the effects of coil motion misalignment on the final measurement result at the 1·10⁻⁶ level. It shows that, at this level of precision, the measured mass value is not dependent on the movement direction of the coil for deviation angles smaller than 0.5° from the gravity vector g, as long as the displacement is measured parallel to g. The experiments have been carried out by tilting the weighing module of the Planck-Balance, which is separated from the displacement measurement module by design. As the moving mechanism – which realises an approximately linear and constrained coil motion – is the same for both modes of the experiment, this is expected, considering the associated mathematical calculations which have already been carried out. Due to the operational effort regarding alignment procedures necessary in most conventional Kibble balances, the reported result is an important step towards broader practical applications, simplifying the implementation of Kibble's principle.