3. Editing Reliability Parameters

Assigning failure rates to an item is a vital part of calculating the reliability of a system. More item failures in a system lead to less overall system reliability. The Reliability editor enables the user to set the failure rate of any component or part.

3.1 Assigning Failure Rates

Failure rate parameters are entered from two locations in the RAM module:

• Criticality & Reliability Editor
• Properties Viewer

To enter failure rates in the Reliability editor:

1. Select Analyses > Criticality & Reliability Editor
2. Select Reliability from the Element Selection drop-down menu
3. Select a component or part in the system tree (e.g. Control Unit)
4. Enter data in the General Reliability & Failure Distribution sections

The example in the guide shows the Control Unit with a duration of operation, mean time to repair, and a Mean Time to Failure of 10,000 hours (equivalent to 100 failures per million hours). Selecting either Exponential or Weibull Failure Distribution type will determine the data used in subsequent reliability analyses. Definitions for Duration of Operation, Mean Time to Repair, Delay Time, and Turnaround Time are found in the MADE Help glossary.

(Figures 8-10: Reliability Tab, Component Selection, Editing Component Failure Rate.)

3.2 Assigning Failure Rates to Parts

Failure rate information for parts is entered in the same way as components, with the exception that duration of operation and Failure Distribution Type are the only options available in the General Reliability section of the Reliability editor (Figure 11: Reliability Editor for parts).

3.3 Failure Mode Ratios (FMR)

While failure rate defines the frequency of an item failure, failure mode ratios (FMR) define the precedence of failure in terms of a ratio. FMRs are used to quantify the importance of a specific FFM (Functional Failure Mode) or Fault and can be applied to components, parts, and part-pairs.

3.3.1 Assigning FMRs to Faults & Failure Modes

Failure mode ratios are a property of component functional failures. The mode ratio information typically comes from test data, OEM data, or published failure mode distributions, e.g. Failure Mode/Mechanism Distributions published by Rome Laboratories.

To assign a failure mode ratio from the Reliability Editor:

1. Select Reliability from the Element Selection drop-down menu
2. Expand the system tree until the desired failure mode or fault is found (Figure 12: FFM Selection)

Selecting a Fault displays a slider. If there are two or more faults in a failure diagram, and the sum of their FMR does not equal one, these values will be normalized. For Functional Failure Modes (FFM), individual Failure Mode Ratios are shown for all failure responses (e.g. high and low) (Figure 13: FMR Slider for Faults; Figure 14: Editing FFM Failure Mode Ratio).

3.3.2 Assign Failure Mode Ratios to Part & Pair Faults

Failure mode ratios for Parts or Pairs can be entered in the Reliability editor in the same manner as component faults (Figure 15: Failure Mode Ratio of a Pair Fault in the Reliability Editor).

Note on Pair Failure Mode Ratios: Pair Functional Failure Modes do not have a Failure Mode Ratio.

3.3.3 Assign Failure Mode Ratios in the Properties Viewer

Another method of assigning failure mode ratios without having to access the reliability editor is by using the Properties viewer while opening the Failure Diagram editor.

To edit failure mode ratio from the Properties Viewer:

1. Open the Failure Diagram editor of an item
2. Select the Properties viewer
3. Select the Reliability tab in the Properties Viewer
4. Select a Fault or Failure Mode in the Failure Diagram editor
5. Edit the Failure Mode Ratio slider or enter a numerical value in the box provided

Example: the Air Filter Fault "Contaminated Fault" is selected in the failure diagram to edit its failure mode ratio (Figure 16: Setting Failure Mode Ratio from the Properties viewer).