Failure diagnosis of discrete event systems: the case of intermittent faults

The diagnosis of "intermittent" faults in dynamic systems modeled as discrete event systems is considered. In many systems, faulty behavior often occurs intermittently, with fault events followed by corresponding "reset" events for these faults, followed by new occurrences of fault events, and so forth. Since these events are usually unobservable, it is necessary to develop diagnostic methodologies for intermittent faults. This paper addresses this issue by: (1) proposing a modeling methodology for discrete event systems with intermittent faults; (2) introducing new notions of diagnosability associated with fault and reset events; and (3) developing necessary and sufficient conditions, in terms of the system model and the set of observable events, for these notions of diagnosability. The associated necessary and sufficient conditions are based upon the technique of "diagnosis" introduced in earlier work, albeit the structure of the diagnosis needs to be enhanced to capture the dynamic nature of faults in the system model. The diagnosability conditions are verifiable in polynomial time in the number of states of the diagnosis.