Application of a digraph model-based approach to system fault diagnostics

The issue of fault diagnostics is a dominant factor concerning current engineering systems. Information regarding possible failures is required in order to minimise disruption caused to functionality. A method proposed in this research utilises digraphs to model the information flow within an application system. Digraphs are comprised from a set of nodes representing system process variables or component failure modes. The nodes are connected by signed edges thus illustrating the influence, be it positive or negative, one node has on another. System fault diagnostics is conducted through a procedure of back-tracing in the digraph from a known deviating variable. A computational method has been developed to conduct this process. Comparisons are made between retrieved transmitter readings and those expected whilst the system is in a known operating mode. Any noted deviations are assumed to indicate the presence of a failure. The digraph diagnostic method is applied to three systems of increasing complexity; a simple water tank, an industrial based test stand of an aircraft fuel system and the Boeing 777-200 fuel system. This research includes transient system effects; the rate of change of a parameter is taken into consideration as a means of monitoring the system dynamically. The validity of the results achieved are evaluated, along with the development of a 'honing-in' strategy to highlight the most probable fault cause for a given abnormal scenario. Finally, the effectiveness and scalability issues associated with the application of the digraph method in system fault diagnostics are addressed.