Hybrid diagnostics requires that the diagnostic reasoner be able to correlate status information from both output functions and failure modes. For example, if a failure mode is ruled out by diagnostics, the diagnostic reasoner must be able to make inferences about the various functions that can be affected by that failure mode, adjusting relative failure probabilities to reflect reduced likelihoods of occurrence (the method of correlating functional and failure mode reliability data is specified in the Failure Probability Calculation Method).
The eXpress diagnostic engine supports the following different types of hybrid inference:
When a failure mode is called into suspicion, all unproven functions that are directly affected by that failure mode are also called into suspicion.
When all failure modes that directly affect a function are ruled out during diagnostics, the function is inferred to be good.
When a function is called into suspicion, all unproven failure modes that directly affect that function are also called into suspicion.
When a function is determined to be good during diagnostics, all failure modes that always affect that function are eliminated from suspicion.
When all functions that are sometimes affected by a failure mode are determined to be good during diagnostics, that function is inferred to be good.
For all hybrid inferences, the relationships between failure modes and output functions is established by defining Affected Functions on the Failure Modes panel for the corresponding object. For inference types 1-3, both "always affects" and "sometimes affects" relationships are taken into consideration, whereas inference type 4 only applies to functions that are "always affected" by at least one failure mode and inference type 5 only applies to "sometimes affects" relationships.
