Reliability HotWire

Issue 104, October 2009

Tool Tips

* What kinds of data results can I display for my predictions in Lambda Predict 3?

Using Lambda Predict 3 you can display many calculated values in the System Hierarchy panel. This makes it easy to scan through the analysis to find the results you need to support your decisions.

You can choose which results you want to display on the System Hierarchy page of the User Setup (File > User Setup). The options for calculated results are:

  • Failure Rate(t) displays the expected failure rate at the mission time, t (hours), as specified in the Mission Time field of the general properties of the top-level item.
  • Failure Rate(t=INF) displays the expected failure rate when the mission time is equal to infinity (i.e. the steady-state failure rate).
  • MTBF displays the mean time between failures, expressed in hours.
  • Contribution displays the contribution made by the item to the failure rate of its direct parent. For example, a value of 0.25 indicates that the item accounts for 25% of the failure rate of its direct parent.
  • Unreliability(t) displays the expected reliability at the mission time, t (hours), as specified in the Mission Time field of the general properties of the top-level item.
  • Standard Deviation(t=INF), for Telcordia SR-332 Issue 2 systems, displays the deviation of the corresponding steady-state failure rate. It is calculated based on the base standard deviation specified in that standard. For more information about this option, refer to the Lambda Predict 3 Users Guide.
  • Failure Rate Upper Bound(t=INF), for Telcordia SR-332 Issue 2 systems, displays the upper confidence bound on the steady-state failure rate. For more information about this option, refer to the Lambda Predict 3 Users Guide.
  • Early Life Factor, for Bellcore/Telcordia systems, displays the ratio of the items early life failure rate to its steady-state failure rate.
  • Based on your inputs in the MIL217 Non Operational window:
    • Non-Operational Failure Rate, for MIL-HBDK-217F systems, displays the failure rate, in failures per million hours, during non-operational phases.
    • Non-Operational MTBF, for MIL-HBDK-217F systems, displays the mean time between failures during non-operational phases, expressed in hours.
    • Non-Operational Contribution, for MIL-HBDK-217F systems, displays contributions made by the item to the failure rate of its direct parent during non-operational phases.
  • Derating, for systems, displays the name of the derating standard applied or, for components, displays the status of the component with regard to derating (i.e. whether the component meets the derating requirements defined in the standard , exceeds the nominal ratings but is not overstressed, or is overstressed according to the derating requirements).

User Setup System Hierarchy Page

* How can I enter classification and mode data in Data Sheets in RGA 7?

In RGA 7, when you are using the Crow Extended model or the Crow Extended - Continuous Evaluation model, you will need to enter information on the failure mode that caused the failure and the classification of each failure mode, where:

  • A indicates that no corrective action was or will be performed (management chooses not to address for technical, financial or other reasons).
  • BC indicates that corrective action was taken during the test or, in the case of multi-phase analysis, at the time of failure. The analysis assumes that the effect of the corrective action was experienced during the test (as with other test-fix-test reliability growth analyses.)
  • BD indicates delayed corrective action. In the case of single-phase analysis, "delayed" means at the end of the test; in the case of multi-phase analysis, "delayed" includes any time after the first occurrence of the failure mode. You will be required to define an effectiveness factor for each BD mode to estimate the fractional decrease in failure intensity once the fix has been applied.

There are several ways to enter this information. You can:

  • Choose the classification from the drop-down list that appears when you click a cell in the Classification column and manually enter the failure mode information in the Mode column.

Entering Information in the Projections Columns

  • Type the classification and mode information into their respective columns. You can type the full classification identifier, or you can enter "C" or "D" in the Classification column and the software will automatically convert your entry to "BC" or "BD."
  • Enter the classification and mode directly in the Classification cell and RGA 7 will parse the data for you. For example, if you have a BC mode that represents a circuit failure, instead of typing "BC" in the Classification column and "Circuit failure" in the Mode column, you can type "dCircuit failure" in the Classification column and then press ENTER to move out of the cell. RGA 7 parses the data and puts "BD" in the Classification column and "Circuit failure" in the Mode column for you.

The last two methods also work when you are pasting data into the Folio.

Note that each unique Mode description must have the same classification wherever it appears in the data set (e.g. you cannot have a BC mode called "Circuit failure" and a BD mode called "Circuit failure"). This also applies to situations in which the modes have been identified by number (e.g. you cannot have a BC mode called "1" and a BD mode called "1").

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