4.3 To Analyse Faults

The concept of reliability expresses the probability that a system (product/service/process) functions as required, and so does not fail, for a predetermined period of time, operating and environmental conditions. Reliability analysis involves the clear identification of the system and the description of a ‘functional diagram’ showing the subsystems, components and their functional interactions, in addition to any external influences on the system, and vice versa.

Once the system has been identified, depending on the specific case, we may adopt an inductive method (also called bottom-up or hardware), with which we start with a postulated fault at the component level and try to identify the effect on the overall functioning at system level. Alternatively, we can use a deductive method (also top-down or functional) where, in contrast with the former, we start from a postulated fault at system level and try to identify all possible causes, up to the level of various components. Among the most popular methods for the analysis of system reliability are the failure mode and effect analysis (FMEA, bottom-up) and fault tree analysis (FTA, top-down).