On the diagnosability of a class of hierarchical state machines

This paper addresses the problem of Fault Detection and Isolation for a particular class of discrete event dynamic systems named Hierarchical Finite State Machines (HFSMs). A new version of the property of diagnosability for discrete event systems tailored to HFSMs is introduced. This notion, called L1-diagnosability, captures the possibility of detecting an unobservable fault event using only high level observations of HFSMs. Algorithms for testing L1- diagnosability are presented. In addition, guidelines are presented for studying the diagnosability of HFSMs that are not L1-diagnosable.