Issue 62, April 2006

Why don’t the failure rates of the system components add up to the system failure rate in Lambda Predict?

It is important to note that failure rates calculated at subsystem, system or project levels are not simply the sum of the failure rates below them in the hierarchy. Lambda Predict takes into account the fact that components are connected to each other. The Connection Type field on the Application tab of components and blocks allows the user to specify how each item is connected. Each connection type is associated with its own failure rate, and this contributes to the higher-level failure rates. For example, in the figures shown next, the connection type for Block 4 is "Reflow Solder."

In the figure that follows, the connection type has been changed to "Spring Contact." Note the change in failure rate for both Block 4 and the system.

In MIL-217 analyses, you also have the ability to define your own connection types. The connections you create will be saved with the project and will be available to you at a later date, or to other users who open the project. The MIL-217 Custom Connections window is accessed by selecting a MIL-217 system, block or component in the System panel and then selecting Custom Connections from the Edit menu. When the window opens, you will notice that two additional connection types have been predefined. In the figure shown next, a custom connection called “My Custom Connection” with a base failure rate of 0.0049 has also been defined. Because this is in the third User Defined field, it will be referred to as “User defined 3” when selecting it for use.

In the figure shown next, the connection type has been changed to User defined 3. Again, note the changes in the failure rates.

How can the status display in the RENO Simulation Console be adjusted?

The Simulation status display gives you information about the progress of the simulation, as shown next.

The variable displayed in the Display Variable Status field is selected on the General page of the Simulation Console, except when you have selected to run multiple analyses. In that case, the display variable is the Result Storage Block that you have selected to maximize or minimize, and its value at the end of the most recently completed analysis is displayed in the Optimal Variable Value field. Other changes you can make to the status display, controlled by the options on the General page of the Simulation Console, include:

• Turn off charting of the simulation by selecting Minimal Display. Only the text progress indicators will be used. Note that if you select this option, no display variable will be shown.

• Change the minimum and/or maximum values used on the Y-axis of the chart using the Y_ and/or ^Y input boxes of the Full Display option.

• Specify the number of increments used to generate the estimated time of completion (ETC) and the progress bar using the Update Increments input box.

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