Abstract: Traditionally, in fault diagnosis systems, the user is instructed to investigate symptoms exhaustively until a single fault is identified. A more advanced known system recognises that it may be cost effective to address a fault that has been determined as being likely but not certain to exist; in preference to further examination of the symptoms. However this technique has been found not to work well when a symptom is known to be only sometimes associated with a fault. The invention addresses this problem by 1) deriving a first value, for each fault, of probable benefit of acting on that fault and for identifying the fault for which that value is greatest, 2) deriving a second value, for each symptom, of probable benefit of an investigation into that symptom and for identifying the symptom for which that second value is greatest, and 3) comparing the greatest first value with the greatest second value thereby determining when to switch from investigating symptoms to acting upon a fault.

Abstract: A fault diagnosis system for diagnosing faults in complex equipment. The system includes means for storing a set of diagnostic signatures which relates a set of known faults which may occur in the equipment to respective fault symptoms which are deemed indicative of said known faults; and means for processing the diagnostic signatures and a set of fault symptoms identified for a current state of the equipment to calculate diagnostic data for identifying a fault causing the current state of the equipment. The diagnostic data includes a plurality of values which are indicative of different relative non-zero likelihoods of each of a plurality of different known faults causing the current state of the equipment.