A Generalization of Hybrid Fault Diagnosability

A hybrid fault situation in a PMC system is a (bounded) combination of permanently and intermittently faulty units. Mallela and Masson [8] have given a general characterization of PMC systems for the diagnosis of hybrid fault situations. For this so-called th/thi diagnosability, when a syndrome takes on a form that is compatible with an allowable permanent fault situation, diagnosis can always be performed that is correct but perhaps incomplete. However, for general hybrid fault situations, syndromes that are compatible with permanent fault situations are exceedingly rare. Hence, th/thi diagnosability makes very limited use of the set of all syndromes that can result from application(s) of the test set. In this paper, a new, broader type of diagnosability for hybrid fault situations is defined and fully characterized. With this new type of diagnosability, at least all the permanently faulty units in a hybrid fault situation can be diagnosed from any syndrome that can result from an application of the test set. Thus, the usefulness of the syndrome space is dramatically increased. Special forms of this diagnosability are presented. Finally, relationships to other diagnosabilities are described.