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Weibull analysis matches historical failure and repair data to appropriate Weibull distributions. These distributions represent the failure or repair characteristics of a given failure mode and may be assigned to failure models that are attached to blocks in a reliability block diagram or events in a fault tree diagram.

Times to failure are converted into estimated reliability values using reliability estimation methods such as Median Rank or those introduced by Nelson.

Computer programs such as AvSim+ and RCMCost automatically fit the selected distribution to the data provided and display the results graphically in the form of cumulative probability plots, unconditional probability density plots and conditional probability density plots. System reliability and availability parameters may then be predicted by constructing reliability block diagrams, fault tree diagrams or failure mode effect and criticality worksheets. Useful parameters may also be computed such as the B Life of a component (the time by which n% of failures would have occurred).

Weibull Analysis Graph

For more information on Weibull analysis, maintainability prediction and theirintegration with other reliability methods visit Isograph's web site at


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