Synthesis Phase Clause Samples

Synthesis Phase. As seen in Figure 15, component failure data relate output deviations to logical expressions that describe the causes of those deviations as component malfunctions and deviations of the component inputs. Each such expression is effectively a mini fault tree that links a top event (the output deviation) to leaf nodes, some of which may represent input deviations. When a component is examined out of system context, input and output deviations represent only potential conditions of failure. However, when the component is placed in a model of a system, the input deviations specified in the analysis can actually be triggered by other components further upstream in the model and the specified output deviations can similarly cause more failures further downstream. This mechanism by which output failures of a particular class at one end of a connection trigger input failures of the same class at the other end results in a global propagation of failures through the system which may ultimately cause significant hazardous failures at the outputs of the system. Given a model of the system and the local safety analyses of its components, it is possible to capture this global propagation of failure in a set of fault trees. These fault trees are mechanically constructed by traversing the model and by following the propagation of failure backwards from the final elements of the design (e.g. electromechanical actuators) towards the system inputs (e.g. material/energy resources, operators and data sensors). The fault tree is generated incrementally, as the local safety analyses of the components are encountered during the traversal, by progressively substituting the input deviations for each component with the corresponding output failures propagated by other components. Figure 16 illustrates the principle that underpins this process of fault tree synthesis. The figure shows a hypothetical motor and its starter circuit as a unit (M) that transforms electrical power provided by a power supply (PS) to mechanical power on a rotating axis.