du/dt Filter, 3AFU400 Series from FUSS EMV. FUSS du/dt-Filters are used to reduce the voltage slew rate at the output of frequency converters to values below 500 V/ s. Features ; Benefits:. du/dt-filters are simple and cheap devices to optimise in a simple drive system. du/dt filters are damping the rate of change of approx. 10.000 V/sec down to a low rate This results in a more smooth running drive system with less noise and increases the long life period of a motor.