An Approach Of Fault Diagnosis Based On Pattenr In Discrete Event System

With the development of industry,the more increasing requirements aboutsecurity amd reliabilty in dynamic discrete event system are needed,the technologyabout based on model diagnosis gradually changes from static systems to dynamicsystems.The research on MBD in dynamic system has become a very important andhot topic,caused large attention of many experts.Discrete event systems in dynamicsystem or equipment fault diagnosis plays an important role,because the discrete eventsystems are close to static systems in each close,and many hybrid or continuousdynamic systems can be represented usinig the discrete event systems. Therefore,researching on MBD in discrete event systems can be as the bridge among staticsystems, hybird and continuous system, as the first research on the hybird system eventhe pure dynamic system about MBD.An improved method of fault diagnosis based on patterns is proposed, dividinginto fault definition, diagnosability analysis and solving diagnostic problems[34]. Inthe research on fault diagnosis methods based on model, firstly we defined the faultsfor system as some sepcial states in system model, and point out the system isabnormal once it is in one of these special states. This method of failure definition isgiven only through quantitative analysis, not the strict qualitative analysis, so theseresearch results only have been applied in theory research stage, not much practicalsignificance. In addition, another method of fault definition is that fault is theabnormal behavior when system’s running,which are descripted by linear temporallogic,called the specification language.But this kind of fault definition based on lineartemporal logic is got by semanticly analyzing system function and systemstructure,strictly dependent on one system, so that one system has its one certain faultdefinition method, and has little contact with its model, leading to constructeddiagnosis system and the definition of diagnosisability has no further application. Wepoint out that every kind of failure patten is defined a regular expression made of a set of system events,this method of fault description makes a fault caused by multipletransfer not one event,which can lead to a detailed relation description.In addition, weimprove the algorithm of fault patten space,which can include all the faultinformation.Using the regular exprenssion descripting the fault,can avoid the highspace problem.Diagnosisability is defined that we can diagnose all the faults when the syetem isrunning according to observation and system model. Diagnosisability analysis isconsidered in the system design stage.When we design a system, we must make itdiagnosisable,so that we do further work for diagnosing system. Regular expressionscan be equivalently transformed deterministic finite automaton with the maturealgorithms, so that fault pattern space can be easily constructed. All the information offaults can be contained in the fault pattern space,which include fault sequences,multiple faults, and intermittent faults. Finally, the definition of diagnosability basedon fault pattern space is given.In the system operation stage,we can establish a diagnosis system for oursystem dynamically or staticly.Observing the system real-timely until the system isabnormal,We can use this diagnosor judge which fault takes place according theoutput information and repair this system timely.One diagnosis can be divided intotwo parts,fault detection and fault isolation.This two parts is a difficult task in large orhuge complicated system.In this parper，we establish diagnosor according systemmodel, fault patten sapce and observation space.An improved method of fault diagnosis based on patterns is proposed. Faults aredefined as patterns that are described by regular expressions to avoid the limitation oftraditionally defining faults which uses ‘special’ events. Regular expressions can beequivalently transformed deterministic finite automaton, so that fault pattern spacecan be easily constructed. All the information of faults can be contained in the faultpattern space,which include fault sequences, multiple faults, and intermittent faults.Finally, the definition of diagnosability based on fault pattern space is given and adiagnostic system is implemented.