The control system for the magnetic suspension comparator system for vacuum-to-air mass dissemination
High precision mass comparisons are typically performed such that both masses are measured under nearly identical conditions. However, there are situations where an artefact needs to be calibrated against a standard kept under different conditions. For example, the new realization of the kilogram will be carried out in vacuum but the majority of calibrations services are performed at atmospheric pressure. At the National Institute of Standards and Technology we have developed an apparatus to perform direct mass comparison under such a condition using magnetic suspension. The stability of the magnetically suspended portion of the system plays a large role in the overall uncertainty of a measurement. Here, the control system for the magnetic suspension and the improvements that have been made to improve stability are described.
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