Hierarchical fault diagnosis system utilizing the signed directed graph and the extended Kalman filter

The hierarchical fault diagnosis system containing a two-level strategy has been developed. This system involves the fault diagnosis method using signed directed graph as a qualitative model-based method and the fault diagnosis method using extended Kalman filter as a quantitative model-based method. In the upper-level strategy, a set of candidates for the cause of failure is obtained by use of the fault diagnosis method using signed directed graph. In the lower-level strategy, the most likely candidate to be the real cause of failure is selected out of the set candidates by utilizing the extended Kalman filter. The efficiency of the present method is demonstrated by applying it to the tank-pipeline system.