||Paoli, A., Lafortune, S.
||Safe diagnosability for fault tolerant supervision of discrete event systems
||Discrete Event Systems; Fault Diagnosis; Fault Tolerant Control; Supervision; Finite State Machine
|The problem of achieving fault tolerant supervision of discrete event systems is considered from the viewpoint of safe and
timely diagnosis of unobservable faults. To this end, the new property of safe diagnosability is introduced and studied. Standard
definitions of diagnosability of discrete event systems deal with the problem of detecting the occurrence of unobservable fault
events using model-based inferencing from observed sequences of events. In safe diagnosability, it is required in addition that
fault detection occur prior to the execution of a given set of forbidden strings in the failed mode of operation of the system.
For instance, this constraint could be required to prevent local faults from developing into failures that could cause safety
hazards. If the system is safe diagnosable, reconfiguration actions could be forced upon the detection of faults prior to the
execution of unsafe behavior, thus achieving the objective of fault tolerant supervision. Necessary and sufficient conditions
for safe diagnosability are derived. In addition, the problem of explicitly considering safe diagnosability in controller design,
termed “active safe diagnosis problem”, is formulated and solved. A brief discussion of safe diagnosability for timed models
of discrete-event systems is also provided.|