Abstract: An improved method of fault diagnosis based on patterns was proposed. Faults are defined as patterns that are described by regular expressions to avoid the limitation of traditionally defining faults which uses `special' events. Regular expressions can be equivalently transformed into deterministic finite automaton, so that fault pattern space can be easily constructed. All the information of faults can be contained in the fault pattern space, which include fault se- quences, multiple faults, and intermittent faults. Finally, the definition of diagnosability based on fault pattern space was given and a diagnostic system was implemented.

Key words: System model,Fault patterns,Diagnosability,Diagnosis problem