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The work described in this paper is part of an investigation of the issues involved in making expert problem solving programs for engineering design and for maintenance of engineered systems. In particular, the paper focuses on the troubleshooting of electronic circuits. Only the individual properties of the components are used, and not the collective properties of groups of components. The concept of propagation is introduced which uses the voltage-current properties of components to determing additional information from given measurements. Two propagated values can be discovered for the same point. This is called a coincidence. In a faulted circuit, the assumptions made about components in the coinciding propagations can then be used to determine information about the faultiness of these components. In order for the program to deal with actual circuits, it handles errors in measurement readings and tolerances in component parameters. This is done by propagating ranges of numbers instead of single numbers. Unfortunately, the comparing of ranges introduces many complexities into the theory of coincidences. In conclusion, we show how such local deductions can be used as the basis for qualitative reasoning and troubleshooting. |
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