To diagnose multiple faults in signed directed graph (SDG) model

an improved signed directed graph (ISDG) multiple fault diagnosis model was proposed. The proposed ISDG model can meet the requirements of multiple faults combinations diagnosis in incomplete information conditions. The diagnosis process in incomplete information conditions can be established by interactive method. The optimum test sequence was determined by the maximal gain-cost ratio. This model improved the efficiency and reduced the cost in the multiple fault diagnosis process. Finally

the multiple faults of an civil engine bleed system were diagnosed with the interactive algorithm. The multiple faults can be diagnosed by ISDG model

so the diagnostic efficiency was improved by diagnosing multiple faults. After using combinational logic

the minimum cost is reduced by 7.25 than the maximum cost

and gain-cost ratio increases by 32.2%. These results explain that the cost can be reduced by 32.2% by using combinational logic.