Minimum and Maximum Fault Detection - two categories of fault detection metrics that are calculated within an eXpress diagnostic study. The minimum metrics are based on the output functions and/or failure modes that would be proven good if one or more tests in the detection sequence were to pass, whereas the maximum metrics are based on the functions and/or failure modes that could cause one or more detection tests to fail (i.e., that would be detected by one or more tests in the detection sequence). In other words, minimum metrics are associated with test coverage, whereas maximum metrics are associated with test interference.
When there is a difference between the minimum and maximum fault detection Test limits that appear in a diagnostic study, this means that fewer functions and/or failure modes would be proven if the associate detection test(s) were to pass than would be detected if the test(s) were to fail. This may not be an issue when the metric describes only one of many detection tests (since other tests in the detection sequence may prove the functions/failure modes that are not proven by that test). When, however, there is a considerable difference between the minimum and maximum fault detection metrics that describe the entire detection sequence (such as Total Functions Detected or Total Probability Detected), this means that the functions/failure modes that are included as interference for tests in the detection sequence are not included in the coverage of other tests in the sequence. In this case, the Analyst should 1) check the test definitions for correctness, 2) determine whether there are other possible tests that can be used to prove the functions/failure modes that are not currently proven by the detection sequence, and 3) determine whether the functions/failure modes in question truly constitute test interference.
In eXpress, the following metrics are expressed in terms of minimum and maximum fault detection:
