Template:Aw statistical properties summary: Difference between revisions

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#REDIRECT [[Distributions_Used_in_Accelerated_Testing#The_Weibull_Distribution]]
===Statistical Properties Summary===
{{aw mean}}
 
{{aw median}}
 
{{aw mode}}
 
{{aw standard deviation}}
 
{{aw cdf and rf}}
 
====The Conditional Reliability Function====
The Weibull conditional reliability function is given by:
 
::<math>R(T,t)=\frac{R(T+t)}{R(T)}=\frac{{{e}^{-{{\left( \tfrac{T+t}{\eta } \right)}^{\beta }}}}}{{{e}^{-{{\left( \tfrac{T}{\eta } \right)}^{\beta }}}}}</math>
 
:or:
 
::<math>R(T,t)={{e}^{-\left[ {{\left( \tfrac{T+t}{\eta } \right)}^{\beta }}-{{\left( \tfrac{T}{\eta } \right)}^{\beta }} \right]}}</math>
 
Eqn. (e137) gives the reliability for a new mission of  <math>t</math>  duration, having already accumulated  <math>T</math>  hours of operation up to the start of this new mission, and the units are checked out to assure that they will start the next mission successfully. (It is called conditional because you can calculate the reliability of a new mission based on the fact that the unit(s) already accumulated  <math>T</math>  hours of operation successfully.)
 
====The Reliable Life====
For the 2-parameter Weibull distribution, the reliable life,  <math>{{T}_{R}}</math> , of a unit for a specified reliability, starting the mission at age zero, is given by:
 
::<math>{{T}_{R}}=\eta \cdot {{\left\{ -\ln \left[ R\left( {{T}_{R}} \right) \right] \right\}}^{\tfrac{1}{\beta }}}</math>
 
This is the life for which the unit will function successfully with a reliability of  <math>R({{T}_{R}})</math> . If  <math>R({{T}_{R}})=0.50</math>  then  <math>{{T}_{R}}=\breve{T}</math>,
the median life, or the life by which half of the units will survive.
<br>
 
====The Failure Rate Function====
The 2-parameter Weibull failure rate function,<math>\lambda (T)</math> ,
is given by:
 
::<math>\lambda \left( T \right)=\frac{f\left( T \right)}{R\left( T \right)}=\frac{\beta }{\eta }{{\left( \frac{T}{\eta } \right)}^{\beta -1}}</math>

Latest revision as of 01:44, 16 August 2012

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