Example 2 - Performing "What-If" Analysis for a MIL-217 System
This example will show you how to perform "what-if" analyses for comparison purposes. For example, you may wish to change one parameter (such as temperature, environment, etc.) to see what impact it will have on the predicted failure rate. You may also want to see how changing a system configuration from series to parallel (i.e., using redundancy) affects the predicted failure rate.
For this example, assume that you are using a MIL-HDBK-217F system to model a power supply unit consisting of one block with a transformer, an external component and an IA, Plated Through Holes block. (The IA, Plated Through Holes block is a special block type with predefined properties for modeling a particular type of construction. Lambda Predict includes several special blocks depending on the standard used.) The IA, Plated Through Holes block contains a low frequency diode, a coil, a capacitor, a micro digital unit, a resistor and a general connector. You also know that the failure rate of the external component is 0.0001 FMPH.
Step 1: After creating the system, Lambda Predict looks like this.
Lambda Predict’s ability to analyze multiple systems within each project allows you to perform "what-if" analyses for comparison purposes. In this case, you will first copy the MIL-HDBK-217F system and then, in the copy, change the ambient temperature at which it operates.
Step 2: Copy the MIL-HDBK-217F system and paste it at the same level as the existing system, then rename it to Test Version.
Step 3: In the System Hierarchy panel, click the 5 VDC Power Supply Module block under the Test Version system, then in the Properties panel, change the value of the Ambient Temperature field to 40 and press ENTER or click outside the field to accept the change.
In the System Hierarchy panel, click the Power XFMR transformer and, in the Properties panel, note that its Ambient Temperature value is now also 40. This is because the 5 VDC Power Supply Module block's Update Children property is set to True and therefore changes to the block's application properties affect its children's application properties as well. Compare the failure rates for the Test Version system to those for the original MIL-HDBK-217F system. Note that the increase in ambient temperature has affected the failure rates throughout the system.
Return the Ambient Temperature value for the 5 VDC Power Supply Module block to 30. The failure rates of the two systems now match.
You can perform other "what-if" tests as well. In the next case, you will see what happens when you change a system from a series configuration to a parallel configuration.
Step 4: Click the 5 VDC Power Supply Module block in the Test Version system. In the Properties panel, change the value of the Redundancy field to True and change the value of the Quantity field to 2, then press ENTER or click outside the field.
Changing the Redundancy value to True means that the system is now in a parallel configuration. There are two of the 5 VDC Power Supply Module blocks present, as indicated in the Quantity field, and only one of those two blocks needs to be functioning at any given time in order for the system to be functional.
In the System Hierarchy panel, note that the value of the Failure Rate(t) field has changed to 3.6633E-05 FPMH from the original value of 0.8736 FPMH, while the value of the Failure Rate(t=INF) field remains at 0.8736 FPMH. The Failure Rate(t) field displays the expected failure rate at the mission time, t (hours), specified in the Mission Time field in the general properties of the item (in this case, 24 hours). The Failure Rate(t=INF) field displays the expected failure rate when the mission time is equal to infinity (i.e., the steady-state failure rate).