Abstract: Vibration induced by electromagnetic forces at an AC power line frequency are cancelled using inertial masses that are oscillated at the line frequency, out of phase with the vibration induced by the electric power due to operation of a machine. The machine can be a rotating device such as a nuclear reactor coolant pump, that is vibrated at component frequencies and harmonics related to the rotational speed and line frequency as well as sum and difference frequencies due to beating of these frequencies together. Cancellation components at the line frequency and it harmonics minimize the generation of annoying sideband acoustic components, which also may contribute to hearing damage. The line frequency cancellation devices preferably include four inertial mass shakers mounted on the outside of the housing of the pump, at 90.degree.

Abstract: A vibration reduction apparatus uses a electromagnetic exciter mechanism to reduce vibrations induced in a machine by a rotating component of the machine. The electromagnetic exciter mechanism employs a magnetic inertial mass coupled in a non-contacting manner externally on a housing of the machine remote from the vibration-inducing rotating component. To operate the electromagnet exciter mechansism, the apparatus employs a vibration sensor attached externally on the machine housing. The sensor senses the vibrations and generates an output signal representative thereof. Also, the apparatus employs signal processing units coupled to the machine for sensing the frequency of an electrical input power signal to the machine which drives the rotating component and generating an output signal representative thereof.