Fault prognostic determines whether a failure is impending and estimates how soon an incident will occur; it is nowadays recognized as a key feature in maintenance strategies. For slowly time-varying autocorrelated fault process, the fault degradation process can be revealed for fault prognostic. Based on this assumption, a fault degradation modeling and online fault prognostic strategy is developed in this paper. A stability factor (SF) is defined to evaluate the changing characteristics of process status and a SF-based non-steady faulty variable identification method is developed to find critical-tofault-degradation variables. A fault degradation-oriented Fisher discriminant analysis is proposed on the selected variables to model the fault evolution process. Uninformative fault effects that do not present degradation are excluded, so that the critical fault degradation information can be focused on. The proposed method is verified by three cases, including a numerical case, cut-made process of cigarette, and the well-known Tennessee Eastman benchmark chemical process.
Index Terms-Fault degradation, fault degradation-orientedFisher discriminant analysis (FDFDA), fault prognostic, nonsteady variable selection, stability factor (SF).