Abstract: A system for measuring the magnitude component corresponding to the once-per-revolution frequency or a multiple thereof of the vibration signal generated by a body rotating at a non-uniform rate. The output of a sensor detecting the acceleration of the vibration motion of the rotating body is decomposed into its frequency components. Simultaneously, the information contained in the output of a tachometer sensor for detecting the rotational speed of the rotating body is used to determine the variation of the rotational speed during the measurement interval. The speed variation information is selectively combined with the frequency components of the acceleration spectrum to yield the magnitude result that would be measured if the rotating body had a constant rotational speed. This method yields vibration information in select frequency bands that is corrected for the non-uniform rate of rotation of the body.

Abstract: A digital ratiometric tracking filter provides superior measurement of the magnitude and phase of vibration of a rotating body, at uniform or non-uniform rotational speed. The sensed speed and vibration signals are concurrently processed and subsequently combined to produce the absolute magnitude and relative phase measurements. The concurrent processing of the sensed signals assures that any system-introduced errors are found in both signals and can be uniformly eliminated by the ratiometric processing thereof.