Trapezoidal Fuzzy Causality Diagram and its Normalization
梯形模糊因果图及归一化研究

Causality Diagram is a probabilistic reasoning method. In this paper, fuzzy set theory is introduced to develop Causality Diagram Methodology after discussing the development and the restriction of conventional Causality Diagram, Fuzzy Causality Diagram can overcome the shortcomings that it is difficult to gain the accurate probability of the event in conventional Causality Diagram. The application of Causality Diagram is extended to fuzzy field by introducing fuzzy set theory. Based on the trapezoidal fuzzy number, operator, fuzzy conditional probability and the normalization method are discussed in this paper. The result of numerical simulating of a subsystem in nuclear plant is coincident with the fact, and it shows the normalizing method is effective. The research shows that Fuzzy Causality Diagram is so effective in fault analysis, and it is more flexible and adaptive than conventional method.