The propagation of faults in process plants: 8, control systems in fault tree synthesis

Studies on the Digraph-Based Approach for Fault-Tree Synthesis. 1. The Ratio-Control Systems

“…1994 American Chemical Society suggested by Chang and Hwang (1992) or Lees (Hunt et al, 1992c) fails to produce correct results due to the presence of unique failure mechanisms not considered before. Notice that still more complicated digraph configurations can be found in other ratio-control systems, e.g., the "full metering control" of the air/fuel ratio to a boiler (Smith and Corripio, 1985) in which a NFFL is coupled with three NFBLs.…”

“…Notice that, although (5) and ( 6) are feedforward loops, the existing techniques (Chang and Hwang, 1992;Hunt et al, 1992c) are not suitable for developing fault trees corresponding to the event r(-l). This is due to the fact that the starting nodes of both loops, m2 and s6, are located on the same NFBL (3) and, thus, their effects cannot be considered independently.…”