Optical device for monitoring critical speeds of a rotating member

Claim 1

An optical device for monitoring critical speeds of a rotating member having a periphery, said device including at least one reflector being arranged on a surface of the rotating member near the periphery of the member to rotate in a circular path, means for directing an input light beam along a path toward a point on the circular path of the reflector to create a reflected beam pulse on a reflected beam path each time the input beam is reflected by the reflector, a light waveguide being arranged on the reflected beam path at an interval from the circular path to receive the reflected beam pulses from said reflector, an opto-electrical transducer being connected to said light waveguide to receive the reflected beam pulses and to convert the beam pulses into electrical pulses, and sound means for generating an alarm being directly connected to an electrical output of said transducer, said sound means comprising a piezoceramic plate with a resonator, said resonator having a natural resonance which is matched to a given pulse frequency of the reflected beam pulses when the rotating member is at said critical speed, said sound means generating an alarm in response to said given pulse frequency of electrical pulses from the transducer so that at normal speeds for the rotating member the electrical pulses applied to the sound means do not create an alarm signal, but at critical speeds the frequency of the electrical pulses is matched to the given pulse frequency and the sound means emits an alarm.