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, a light source producing an input beam, means for directing the input beam toward a point of the circular path of the reflector at a given angle of incidence, a light waveguide being arranged at a suitable interval from the circular path and at a suitable angle to receive a reflected beam from said reflector which occurs when the input beam is reflected by said reflector, and an opto-acoustical transducer being connected to said light waveguide to receive the reflected beam and convert light pulses into sound, said opto-acoustical transducer being provided with a resonator, which exhibits a natural resonance which is matched to a pulse frequency of the reflected beam produced by the reflector when the rotating member is at a critical speed so that when the rotating member reaches the critical speed, the transducer with the resonator emits an acoustical alarm.