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Keeping the ripple of power-supply currents within the specification limits is crucial for the beam stability of the BESSY storage ring. Malfunctioning or aged electronic devices cause an increase of output ripple over the years. This increase is hardly noticed by the operator or operation analysis because the slow integrating AD converters for the current readbacks filter out the ripple. Furthermore, it is almost impossible to find the connection between certain beam movements or beam noise and the faulty power supply causing it. To improve this situation, ripple information for every power supply is required within the control system. The latest series of the CAN bus-connected power-supply interface cards used at BESSY provide an additional fast AD converter. With a sampling frequency of 83.5kHz, this ADC samples ripple information over one period of the mains voltage. The results are transferred over the CAN bus to the EPICS-based control system and can be processed in the usual ways. Using this setup, even temporarily increased ripple can be detected without complex measurement methods.
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