Isolation Probabilities Using Testing Only - Cum % Column
Description
This column is listed under the Isolation Probabilities Using Testing Only label in the Fault Group Size Percentages section of the Fault Isolation Report. Each entry in this column contains the cumulative probabiity that an isolated fault group will contain no more than the number of replaceable items indicated in the corresponding row in the Size column. This metric is frequently used to satisfy the fault isolation component of contracted testability requirements.
Calculation
This Test limit can be calculated by summing the aggregate failure probabilities associated with each isolated fault groups that is no larger than the given size, and then dividing this sum by the Total Probability Detected. This calculation method can be expressed using the following equation:
where
x
=
the specified number of replacement items (Size column)
Alternatively, this metric can be calculated by summing the incremental isolation probabilities (the Test limits in the corresponding % column for all rows up to and including the current row), as shown in the following equation:
where
x
=
the specified number of replacement items (Size column)
IsoPrT(i)
=
the probability that a failure is isolated to a fault group containing x replacement items (% column)
