Computation of minimal diagnosis bases of Discrete-Event Systems using verifiers: Method of the ambiguous cyclic paths

In order to diagnose the occurrence of a fault event of a Discrete-Event System (DES), it is first necessary to verify if the language of the system is diagnosable with respect to an observable event set and a fault event set. If the language of the system is diagnosable, then a diagnoser can be implemented. In some cases, the language of the system remains diagnosable even if some events of the observable event set become unobservable. This leads to a reduction in the number of sensors used in the diagnosis, therefore reducing the cost of the system. Another possibility is to exploit the redundancy of some sensors in order to obtain a more reliable and robust diagnosis. In this work, we propose an algorithm to find, in a systematic way, all minimal subsets of the observable event set that ensure the diagnosability of the DES (minimal diagnosis bases). The method is based on the construction of verifiers and has lower computational complexity than another method recently presented in the literature.