Alignment in the MSL Kibble balance

This paper discusses the alignment aspects of the MSL Kibble balance, which is based on a twin pressure balance setup. This novel design utilizes the features of the piston-cylinder unit in a pressure balance, where its strong self-centring force can provide a well-defined axis for the moving coil. Here we present the MSL Kibble balance in terms of its design features and operation, effects of misalignments of the piston-cylinder unit and requirements to mitigate this. In particular, we model the righting moment of the piston-cylinder system and show how this is essential for the alignment and operation of this Kibble balance.