Is there an easy way to estimate the parameters of a distribution when you cannot obtain their values from data?
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Yes, the Quick Parameter Estimator (QPE) helps you to estimate the parameters of a distribution based on information you have about the behavior over time. This can be the time-to-failure, time-to-repair, time for a maintenance crew to arrive, etc.
In all Synthesis applications, you can open the QPE from the Model window or the Model wizard by clicking the QPE icon.
In Weibull++/ALTA, it’s also accessible from the Home tab of the Ribbon and several analysis interfaces (including the Weibull++ standard folio, the Weibull++ Monte Carlo and SimuMatic utilities, and the Expected Failure Times plot).
The QPE allows you to choose a life distribution and then estimate its parameters by using one of two quantification methods:
- Enter one unreliability value and an estimated value for one of the parameters. This approach solves for the value of the remaining parameter(s).
- Enter two unreliability values at specified mission times. This approach obtains estimates for all the parameters.
For example, let’s say that the unreliability of a certain product is estimated to be 50% at 100 hours and 99% at 300 hours. If you have reason to believe that the failure behavior follows a 2-parameter Weibull distribution, you can use the QPE to estimate both parameters, as shown next.
If you are not certain which distribution would best represent the failure behavior, you can click the Use Wizard button at the bottom of the window.
The Wizard view will ask you to choose among three different types of models that you can build with the QPE, and then ask more specific questions about your selected model. Based on your responses, it will automatically select a distribution and estimate its parameters.
For example, if you choose to build a reliability model, you will need to supply the following information:
- How age affects the product’s reliability.
- The product’s intended design life and the estimated warranty life.
- Best-case, worst-case and most likely unreliability estimates for the product at the end of the design life and warranty time.
The QPE will return a model based on the information you provide.