Patent ID: 7866213

Claim:
A method of identifying an unfolded non-synchronous blade vibration frequency in blades on a rotating rotor using a plurality of sensors spaced from each other about the rotor, said method comprising the steps of: acquiring a set of data from said sensors comprising measurements of blade passing events obtained during a predetermined number of rotor revolutions; processing said set of data using a Fourier analysis to generate an output representative of frequencies and phase shift angles corresponding to blade vibrations; identifying a subharmonic frequency width based on a rotational speed of said rotor and said predetermined number of rotor revolutions; generating a phase shift slope from said Fourier analysis output defined by a change in blade vibration wave phase shift with respect to a displacement between an initial blade passing event sensed by one of said sensors and one or more subsequent blade passing events sensed by one or more of said sensors for passage of the same blade; identifying a fold down subharmonic for a blade vibration mode using said phase shift slope; and generating an output comprising said non-synchronous blade vibration frequency using said subharmonic frequency width and said fold down subharmonic.