Fault diagnosis in analogue circuits using AI techniques

The authors describe a technique for detecting and locating faults in analogue circuits by checking that the measurements are consistent with the circuit function. The unique representation used accommodates the imprecise nature of analogue circuits. A model of the circuit is formed from the constraints imposed by the behavior of the components and the interconnections. The values of parameters within the circuit are deduced by propagating the effects of measurements through this model. Faults are implied from the detection of inconsistencies and located by suspending constraints within the model. The method does not use fault simulation and is therefore applicable to any type of fault. It is able to detect performance variations, as well as catastrophic failures. Values are represented as ranges within which the true value lies. This overcomes the difficulty of representing the uncertainty inherent in any analogue design or measurements. The method has been successfully used to detect and locate a number of faults in several circuits