For the top-level assembly, the value for Failure Rate, Predicted is obtained using the mean failure rates and standard deviations for all parts in the system. The calculation does not use the failures rates and standard deviations for any subassemblies that exist in your system. The results shown at the subassembly level are for informational purposes only. They are not factored into the predicted failure rate calculated for the top system level.

All parts are considered to be independent. For example, assume System 1 has one resistor with a quantity of 2. Assume System 2 has two resistor part records, each with a quantity of 1. The overall system level results are the same for both System 1 and System 2.

When a value is entered for Failure rate, specified for the part, then this failure rate is assumed to be its mean failure rate and is shown in Failure Rate, Mean. The value for Failure Rate, Standard Deviation is assumed to be zero, which makes Failure Rate, Predicted and Failure Rate, Mean equal.

Standard deviation specified is available for use with the Telcordia Issue 3 or Issue 2 model. In this field, you can enter a standard deviation for an assembly or part with a specified failure rate or MTBF value. This field appears in the following Prediction panes:

Additionally, you can use the Format Builder to insert the this field in the System Tree Items table or Parts Table.