Fault Detection and Diagnosis Through Signed Diagraph

With increasing automation in chemical processes, occurrences of faults are very common now a days. An undetected fault can escalate out of proportion and cause massive losses to an industry in terms of infrastructure and personnel. The signed directed graph (SDG) technique has been widely used for diagnose the fault mainly because of its resemblance to a human way of reasoning, its thorough analysis of abnormal situation, and its ability to present a complete description of all process variable effected by a fault. SDG represents the causality between the processes variables involved in system. Case studies including double effect evaporator, multi stream controlled CSTR and a plant wide flow sheet for reaction separation process have been considered. To construct the SDG of a system either arc value calculation or perfect matching is performed. Here SDG is constructed for systems with and without control loop. To diagnose the fault, backward reasoning approach and incipient fault diagnosis (IFD) are used. A quantitative simulation is also performed to validate the proposed SDG technique in identification of fault.