Optical method for instant estimate of vibration signature based on spectrum analysis of phase-modulated light pulses

The method is presented for instant estimation of vibration signature based on spectrum analysis of phase-modulated (PM) light pulses. The light pulses are reflected from optical markers on the machine shaft and illuminated with the narrow light beam. The pulses are phase modulated by the shaft vibration. Due to the low modulation index, the PM sidebands are the true image of the vibration spectrum. The method is useful for instant estimation of vibration signature on machines that are not instrumented for shaft vibration measurement and where the casing vibration does not give the signature of rotor dynamics.