Qualitative analysis in simulating analog circuits

The authors address the problem of troubleshooting analog circuits. An expert system prototype is presented, capable of diagnosing faults by means of a qualitative analysis of the circuit being examined, i.e. by considering the values of quantities not in exact terms but in terms of belonging to prefixed intervals. The proposed system pursues the modern approach to realizing expert systems, in the sense that, unlike the early solutions in this domain, it exploits not only shallow knowledge (e.g. production rules) but also, and especially, deep knowledge about the behaviour of the individual components, the circuit topology, and the laws of electrotechnics. The problem of diagnosing analog circuits is formalized and its basic features are illustrated in relation to the qualitative analysis procedure. A details account of the expert system is then provided both from a conceptual point of view and in regard to its implementation in Prolog, and its advantages, limitations, and possible developments are discussed