After analyzing the information transfer characteristics of large-scale complex systems,a new fault description model-fuzzy probability signed directed graph(FPSDG) was proposed by introducing the status association probability,fuzzy information and object-oriented technology in SDG.

Signed Directed Graph (SDG) is used for a mathematical model representing the influences among elements of the system, which considers the characteristic of system’s structure and can deal with the complex process of system in a large-scale, and it is a self-contained method to diagnosis system failures.

There are two topics about the method being given: fault propagation digraph and signed directed graph( SDG) .

Algorithms of SDG-based Fault Diagnosis with Unmeasured Nodes for Deaerator;

Application of SDG in Chemical Hazard Assessment

On the basis of analyzing the theory of signed directed graph(SDG)technology,practical application of SDG qualitative model in computer aided HAZOP and fault diagnosis was discussed.

The former method derives rules through rough set reduction of a genetic algorithm,while the latter transforms the cause-effect graph to rules by using the automatic reasoning result of a signed directed graph(SDG).

The process signed directed graph(SDG) model represents the cause and effect linkages to connect the fault origin to the observed symptoms of the fault.

In view of the characteristics of modern chemical process flow,this paper models the process flow of chemical production by utilizing Signed Directed Graph(SDG) model,and obtains causality diagram that describes the mechanism of process flow.