Method for detecting spectral changes in the frequency domain

The use of frequency response estimates for change detection is considered. The class of faults considered affects the spectral properties of the system. Spectral changes are detected as deviations in the frequency response, through the choice of a suitable residual. Taking into consideration the statistical nature of a finite-time estimator, a χ² detector is then designed for the residual. The performance of the fixed sample size detector is compared with a conventional cumulative sum algorithm, and found to be better. A DC motor is used as an implementation example to illustrate the performance and properties of the detector.