Multiple-fault diagnosis under uncertain conditions by the quantification of qualitative relations

Among many fault diagnosis methodologies for chemical processes, the signed digraph (SDG) offers a simple and graphical representation of the causal r elationship between process variables and has been widely used. The assumpt ions of SDG such as single-fault assumption and consistent path assumption, however, have limited its applications to real processes. This paper prese nts a multiple-fault diagnosis methodology utilizing many advantages of SDG . The diagnosis model is organized by carefully modifying SDG and searching the fault propagation path. The on-line diagnosis is performed through qua ntifying the qualitative relation of the fault propagation path, and this q uantification enables the diagnosis to overcome the weakness of SDG under u ncertainty and to diagnose multiple faults. Also, this work suggests how mo dified-CUSUM (cumulative sum) can be used to handle compensatory or inverse response. The proposed methodology is illustrated with a case study of a c ontinuously stirred tank reactor (CSTR) with a heat exchanger.