Exact, almost and delayed fault detection: An observer based approach

This paper considers the problem of fault detection and isolation in continuous- and discrete-time systems while using zero or almost zero threshold. A number of different fault detection and isolation problems using exact or almost exact disturbance decoupling are formulated. Solvability conditions are given for the formulated design problems together with methods for appropriate design of observer based fault detectors. The l step delayed fault detection problem is also considered for discrete-time systems. Moreover, certain indirect fault detection methods such as unknown input observers, eigenstructure assignment, factorization, and parity equation approaches are generalized by including the almost estimation methods in addition to exact estimation methods.