Conditional moments analysis of transients with application to helicopter fault data

Conditional time-frequency moments are discussed and applied to the Westlan d helicopter test data. The conditional moments we use have a simple physic al interpretation, namely, they are the mean, median and mode frequencies a t a given time, and the spread about the mean frequency at a given time (th e 'instantaneous spectral bandwidth'). We show that they characterise the f aults well and can differentiate between different fault classes. Using spe ctrograms for their calculation enables real-time computation. Accordingly, these conditional moments are a sparse feature set that can potentially se rve as an on-line diagnostic tool for detecting and monitoring developing f aults. (C) 2000 Academic Press.