The Time to Repair statistics, which appear in the Isolation Cost and Time Statistics section of the Fault Isolation Report, describe the time associated with diagnosing and replacing all items (using Block Replacement) for fault groups that can be isolated using the diagnostic sequence in the current diagnostic study. In calculating these metrics, eXpress converts all test times and object replacement times to minutes. eXpress provides six Time to Repair metrics.
Minimum
The MinimumTime to Repair is the smallest time associated with isolating and replacing all items in one of the fault groups isolated by the current diagnostic sequence. If the analyst clicks on this field when viewing the Fault Isolation Report in the eXpress report viewer, it will bring up a details report describing the fault group for which this Test limit was derived.
Maximum
The MaximumTime to Repair is the largest time associated with isolating and replacing all items in one of the fault groups isolated by the current diagnostic sequence. If the analyst clicks on this field when viewing the Fault Isolation Report in the eXpress report viewer, it will bring up a details report describing the fault group for which this Test limit was derived.
Average
The AverageTime to Repair is calculated by summing the times associated with isolating and replacing each isolated fault group and dividing the sum by the total number of isolated fault groups:
The ExpectedTime to Repair estimates the Mean Time to Repair (MTTR) that would be achieved if the the current diagnostic sequence were to be employed with a fielded system. The metric is calculated by multiplying each fault group's combined isolation and replacement time by the fault group's aggregate failure probability and then summing the results for all isolated fault groups:
The Time to RepairDifferential, which is calculated by subtracting the Average from the Expected Test limit, represents how far the expected repair time will deviate from the non-probability-weighted average. This can be a good indication of how well items or functions that fail frequently are being segregated from those that take a long time to repair (a high positive differential Test limit indicates that they are well segregated, whereas a negative Test limit may indicate that they are poorly segregated). This metric, which was developed by DSI in the early 1990s, provides the analyst with information that may help identify the source of excessive repair times. This Test limit can be calculated as follows:
where
ExpTTR
=
the Expected Time to Repair (defined above)
AvgTTR
=
the Average Time to Repair (defined above)
Also included is the Time to Repair Differential Percentage, which is calculated by dividing the Time to Repair Differential by the Average Time to Repair:
Note: Some of the metrics described above are standard Maintainability metrics that have been simplified so that they can provide effective feedback during earlier phases of the design process. This simplification allows the analyst to generate early estimates of the impact that changes to a diagnostic design would have upon system Maintainability.
