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A signed directed graph (SDG)-based computation procedure is proposed in this paper to predict the effects of one or more fault propagating in a multiloop process system. The conventional version of qualitative simulation techniques is modified to identify not only the locations of fault origins but also their magnitude levels. In addition, a computer algorithm is presented to generate the IF−THEN inference rules automatically according to the anticipated fault propagation behaviors. The effectiveness and feasibility of this approach has been tested with three case studies. Two of them are concerned with level control systems and the other an exothermic continuously stirred tank reactor (CSTR) with temperature and level control loops.

The diagnostic resolution issues are usually addressed with a quantitative or semiquantitative approach in the reported studies concerning sensor placement procedures. Since the required information for implementing the traditional methods may not be always available, a SDG-based strategy is proposed in this paper to design the sensor networks on the basis of qualitatively predicted fault evolution sequences. To achieve a maximum level of resolution and, at the same time, to ensure observability, the corresponding design problems are formulated as integer programs in this work. Two alternative strategies are also developed for producing the optimal solutions. The feasibility of the proposed method is demonstrated with three examples.

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