Duty cycle lists allow the Analyst to define sets of factors by which the raw failure ratescan be multiplied to account for different levels of usage (duty cycles) within a design. An Operating Mode can then be set up to use that duty cycle list. When the Operating Mode is used in a diagnostic or FMECA study, the raw failure rate for each object and/or output function will be multiplied by the corresponding factor (percentage) in the duty cycle list as the adjusted failure ratesused within the analysis are calculated. There are two situations in which this capability can be particularly useful:
Scaling Local Failure Rates - when a failure rate is given in terms of an individual object's usage (such as when an engine's failure rate is defined as failures per million hours of engine use), a duty cycle list can be used to adjust the raw failure rate so that it represents failures per million hours of systemuse. In this case, the factor that corresponds to that object (the engine) would be set to the overall percentage of system time in which the object is used.
Adjusting Failure Rates to Account for Different Operating Modes - when an individual object or function's failure rate must be modified to account for a particular mode of system operation, a duty cycle list can be used to adjust the raw failure rate. Here, the factor that corresponds to that object or function would be set to the value by which the raw failure rate must be multiplied in order to accurately reflect usage in the given Operating Mode.
Duty cycle lists, which are hidden by default, can be displayed by choosing "Duty Cycle Lists" from the Explorer Tree submenu within the View menu. The top-level "DUTY CYCLE LISTS" folder (containing the baseline duty cycles list) will then appear in the Explorer Tree:
