Failure Rate Calculations

Failure Rate Calculations

Table of Contents Performing Failure Rate Calculations... 1 Prerequisites for Performing a Failure Rate Calculation... 1 Failure Rate Flags... 1 Finding Problem Parts... 1 Failure Rate Return Codes... 1 Setting User Set Failure Rate Flags... 2 Setting a User Set Failure Rate for a Component... 2 Setting a User Set Failure Rate for a Subassembly... 2 Setting User Set Failure Rates for Many Components... 3 Clearing User Set Failure Rate Flags... 5 Performing the Calculation... 5 Index... 7 iii

Performing Failure Rate Calculations Prerequisites for Performing a Failure Rate Calculation Prior to performing a failure rate calculation: Build the project tree in the Reliability Manager. The project tree defines the parent/child relationship of the various assemblies and parts. You are then ready to perform the failure rate calculation on each assembly, working towards the project node. Failure Rate Flags The following table shows the meaning of the flags that appear to the left of the node after a failure rate calculation: Flag Next to Node Name: Green check Blue check Yellow question mark Red X Minus sign Finding Problem Parts Means: Failure rate calculated successfully. The failure rate calculation includes one or more user set values. The failure rate calculator used default values. A problem prevented the failure rate calculation. Failure rate has not yet been calculated. After trying to calculate a failure rate and getting an unsuccessful return code, you will want to locate the components that are causing a problem with the failure rate calculation. To find the problem components: 1. Click on the subassembly or board where you want to check the components. 2. Click on the Parts List tab and scroll to the "Op Status" field. 3. Scan the list of failure rate return codes for fatal codes such as "Overstressed Part," "Unable to calculate," etc. For a list of the return codes, see Failure Rate Return Codes As part of the failure rate calculation, you can generate a troubleshooting report. See Viewing the Troubleshooting Log Failure Rate Return Codes Failure rate return codes give a variety of information about the failure rate calculation. The most severe error code rolls up to the next level. The return codes are displayed in the Status" field or the Assy Data or Part Data tab. The return codes include: Return Code: Invalid User Set Value Overstressed Part Part not in FR-Method Document Means: The user set value is invalid or the field is blank. The failure rate couldn t be calculated because of one or more overstressed parts. The part type is not comprehended by the FR prediction method selected 1

Failure Rate Calculations Success Unable to Calculate Used Default Values Used Extrapolation User Set Value for this project. The failure rate was calculated successfully. Invalid applied parameters. The failure rate was calculated successfully using default values. Parameters needed were outside the table values in the FR_Method Document. The tool extrapolated values to use in the calculation. The failure rate was user set. Setting User Set Failure Rate Flags Failure rates can be user set for components, boards, subassemblies, or the entire project. If a value has been user set, then running the failure rate calculator will have no effect on the failure rate for that node. Setting a User Set Failure Rate for a Component 1. Select the component. 2. In the Operating data group portion of the Part Data tab, find the "Failure Rate" field. 3. Click to place an "X" in the small box to the right of the field. The return code in the "Status" field displays "User Set Value." 4. Enter a value in the "Failure Rate" field. 5. Click on Save. You are now ready to run the failure rate calculation using the user set value. Setting a User Set Failure Rate for a Subassembly 1. Select the subassembly. 2. To set the operating failure rate find the "Failure Rate" field in the Operating section of the Assy Data tab. Like wise, if you want to set the Storage & Dormancy failure rate, find the Failure Rate Field in the Non-Operating section of the Assy Data tab. 3. Click to place an "X" in the small box to the right of the field. The return code in the "Status" field displays "User Set Value" and the failure rate field and MTBF button become selectable 2

Performing Failure Rate Calculations 4. You can enter a value directly in the "Failure Rate" field, or if you prefer, you can enter the failure rate as a MTBF by pressing the MTBF button. A panel is displayed that will allow you to enter a value for the MTBF. When you click OK after entering a value, the value is converted to a failure rate and placed in the failure rate field. 5. Click on Save. You are now ready to run the failure rate calculation using the user set value. Setting User Set Failure Rates for Many Components Use this menu item to set the failure rates and failure rate calculation method for many components. This is useful when you calculate failure rates using multiple methods or when you want to change the failure rate for a number of 'Miscellaneous' parts. 1. Select the subassembly or board. 2. Click once with the right mouse button. The pop-up menu is displayed. 3

Failure Rate Calculations 3. Select Set/Unset FR / Method. 4. In the Available Parts list, select a component to add. Note that all project parts display, but only parts on the current node and its children will be affected. 5. Click on Add. The component displays in the list to the right, labeled Selected Parts. 6. Continue until all components that you want to modify are added. 7. Under Failure Rates, select the type of Failure Rate (Op or Nonop) of interest. 8. Under Set/Unset, select the item you want to modify. The "Set FR Method" sets the calculation method. It works in conjunction with the pull down list of available calculation methods. 4

Performing Failure Rate Calculations The 'Unset FR Method' removes the method from the parts, which will then use the FR Method identified for the parent assembly. The "Set FR to" button works with the input window on the bottom row. Type in the value of the failure rate that is to be assigned to the selected parts. 9. Select the depth for setting the user set failure rate flags. "Current Assembly Parts" sets failure rate or method for each component on the selected assembly only. "Include Subassemblies" sets the failure rate or method on the selected assembly and for all subassemblies (children). 10. Click on 'Ok'. Clearing User Set Failure Rate Flags You can clear user set failure rate flags for both subassemblies and individual parts. If you want to clear the user set failure rates for selected parts, use the Set/Unset User Set FR Flags option. See Setting User Set Failure Rate Flags. The following procedure uses a subassembly as the example. To clear user set failure rate flags: 1. From the Reliability Manager, select the node or part where you want to clear the user set failure rate flags. 2. Click once with the right mouse button. 3. Select the Clear User Sets option. The following window displays: 6. Click on OK. 4. In the top box, select the items to clear. 5. In the Clearing Depth box, select the depth to which the user set failure rates are to be cleared. "Connection and Parts" clears the user set failure rates for connections and parts in the selected assembly only. "Include SubAssy" clears user set failure rates for the assembly you selected and all assemblies and boards that are children of that subassembly. The Project Tree redisplays with the "Failure Rate" field and the associated checkbox in the data group you selected (Operating or Non-Operating) blank. Performing the Calculation 5

Failure Rate Calculations To perform the failure rate calculation: 1. Select the node or part of interest. 2. Right click with the mouse to bring up the pop-up menu. 3. Select 'Calculate Failure Rates'. 4. The main panel of the Survey Tool is presented. See Using the Survey Tool for detailed instructions on the capabilities of this tool. Calculating a Part - Quick Calculation You can perform a quick calculation for a part by selecting the part from the product tree and then electing the Pi-Factors Tab. This will present all the failure rates, Pi factors and diagnostics for the currently selected variable and static data. It will not update the failure rate of the part, so it is handy as a sensitivity analysis where you can jump between tabs, change input data and see the immediate result of the change. 6

Index C Clearing User Set Failure Rate Flags... 5 F Failure Rate Flags... 1 Failure Rate Return Codes... 1 Finding Problem Parts... 1 P Performing the Calculation... 6 Prerequisites for Performing a Failure Rate Calculation... 1 S Setting User Set Failure Rate Flags... 2 7