Fault Isolation Requirements
During the calculation of MTBF in a MIL-HDBK-472 Procedure 5A calculation, an S factor is required. The S factor is used to compute the average number of replaceable items (RIs) in a fault isolation result or the average number of iterations required to correct a fault. The S value can be user-defined or estimated based on values entered in the table in the Fault isolation requirements area. This area is available only when fault isolation ambiguity is estimated.
When using the estimation table to compute the S factor for the group, the data is expected in the form:
X 1 % <= N 1 RI s, X 2 % <= N 2 RI s, X 3 % <= N 3 RI s … 100% <= N n RI s
Where X 1 % < X 2 % < … < 100%
If the data is specified in the form that follows, it is first converted to the expected form.
X 1 % to <= N 1 RI s,
N 1 RI s < X 2 % <= N 2 RI s
N 2 RI s < X 3 % <= N 3 RI s
….
N n − 1 RI s < X n % M = N n RI s
The following table describes the conversion process.
Value to Enter | Convert by |
|---|---|
X 1 | X 1 |
N 1 | N 1 |
X 2 | X 2 + X 1 |
N 2 | N 2 |
X 3 | X 3 + X 2 + X 1 |
N 3 | N 3 |
… | |
X n | X n + X n − 1 + X n − 2 + … X 1 |
N n Where (X n + X n − 1 + X n − 2 + … X 1 = 100) | N n |
For information about how Procedure 5A calculates MTTR, see MTTR Calculations per Procedure 5A.