Weibull influence of suspensions

Suspensions are units in a Weibull life test are units that are still functional or are failed by different failure mode. In a weibull analysis all the units in the analysis must have the same failure mode. If different failure modes are not suspended the weibull line fit will be poor. For more information of different failure modes in one plot see here. Units that are suspended will have in influence on the weibull curve.
To get some understanding of the influence look at the weibull graphs below. In the table suspended units are marked gray.

Data file

• Suspensions at the
  Start
  of a life test result in a steeper curve (higher beta) and a higher characteristic life (higher eta).
• Suspensions at the
  middle
  of a life test result in a less steep curve (Lower beta) and a higher characteristic life (higher eta).
• Suspensions at the
  End
  of a life test result in a slightly steeper curve (higher beta) and a slightly lower characteristic life (lower eta).
  

So we can also conclude that measuring when a unit fails at the beginning of a life test is very important for a good Weibull curve!

How mark units as suspended

Mark units as suspended by selecting cells and right click on the selected cells and select suspensions from the drop down list.

Legend

η (eta) = Characteristic life (63.2% of the samples will have failed)
β (beta) = slope of the weibull plot
n = amount of samples the units in test