Process Fault Analysis Using Signed Directed Graphs and Fuzzy Logic

Abstract

Now-a-days in modern industries, the scale and complexity of many systems are increased continuously. These systems are subjected to low productivity, system failures because of mis-operation, external disturbance or sometimes control system failure which often gets out of control and leads to huge destruction in terms of infrastructure and personnel. When a fault is detected the next steps to follow are identifying the root cause of the fault, determining the extent to which the system functioning can be maintained despite of the fault and to find a suitable solution or repair to the fault. Hence at present, fault diagnosis is required for a large and complex system of industrial processes. Compared with the classic fault detection of local systems, the fault detection for complex systems concern more about the fault propagation in the process systems. This demand is much close to hazard analysis which is a kind of qualitative analysis. Signed Directed Graph (SDG) is a kind qualitative graphical model which can be applied for fault diagnosis. Also in this paper another alternate method for qualitative process modeling which uses fuzzy graph theory based on SDG known as Fuzzy-SDG to qualitatively represent the process systems. SDG and Fuzzy- SDG has been applied to various systems in this paper and their effectiveness was observed. Various systems that have been studied are: Feed Back Control system, Cascade control system, Dual averaging control system and three element control system. Using the working principle of each process and theoretical knowledge, SDG was developed for each process. Also Fuzzy Signed basics were also studied. The main advantage of linking fuzzy logic with the signed directed graph is that it will give more efficient way of resolution of fault diagnosis in process industries.