Periodic revs altering device has control unit producing signal by which revs e.g. of ventilating fan are periodically altered

摘要

The revs altering device consists of a control unit (10) arranged to produce a signal by which the engine revs can be altered periodically. The control unit produces a signal by means of which the revs of the motor (18) are periodically altered in at least one preset revs range. The signal may be based on frequency or amplitude.