Creating signed directed graph models for process plants

The concept of qualitative modeling is briefly described. This paper focuse s on the use of signed directed graphs to model fault propagation in proces s plants. It is common to use a unit-based approach for modeling. Two kinds of problems, which arise when constructing unit-based qualitative models, are identified: (1) The models are difficult to construct. (2) Ambiguities due to multiple causal paths may occur when the models are combined. A meth od that allows models to be built simply and correctly is proposed. The met hod incorporates features from the knowledge acquisition field, and a compu ter-aided modeling tool, Equipment Model Builder, has been built to support this method. A new modular approach is presented which overcomes the probl em of ambiguous inference when qualitative models are combined. Two case st udies were used to evaluate the method developed and the support tool.