Dynamic analysis of qualitative circuits for failure mode and effects analysis

There are a number of reason for wanting to generate FMEAs as soon in the design process as possible; three of the more notable being safety, reliability and cost. The Flame system provides electrical engineers with a means of automating FMEA using, amongst other techniques, qualitative circuit analysis. Until recently, the qualitative circuit simulator with Flame has only been able to generate failure descriptions for circuits containing a set of relatively simple components; for example, bulbs, resistors, connectors, wires and switches. Representing and reasoning about the operation of CPUs, multi-way switches, sensors, multi-speed motors, and other complex components was not possible due to their intricate effect on a circuit. The paper describes how the behaviour of such components and their failure modes can now be represented; and gives an example of analysing a central door locking circuit containing such complex components. The technology which has facilitated such advances is the dynamic analysis of qualitative circuits. This allows the circuit analyser in Flame to represent and reason about dependencies within a circuit; for example, a relay switch state depends on the state of the coil, and ECU output on the state of the inputs. Because of these advances, Flame can now perform FMEAs of large complex circuits-as found in modern automobiles.