3-Parameter Weibull

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• #39108

Chen
Participant

Can one of you explain me, in a few simple short lines, the concept 3-Parameter Weibull distributions and where (processes) to expect them?
On research on a deformation process of PTFE (synthetic material) every time Minitab gives “3-Parameter Weibull” when I perform an distribution identification.
Bernard

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#118268

Paul Gibbons
Participant

Hi,
I am not sure if it is the same thing but I have carried out Weibull plotting of the reliability of plant. In the plot you get 3 separate distributions. One is based on quick breakdowns, e.g.a fuse blown, the second is based on longer breakdowns, e.g. motor burnt out and the third is based on the major breakdowns, e.g. a gearbox and drive system.
I think the Weibull, in this example, has highlighted the different time levels in relation to the different levels of reliability of plant. Perhaps the PTFE process has 3 different levels of something in relation to something, if you know what i mean?
Hope this helps, if not please do not crucify my example all you Weibull experts ;¬)
Paul

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#118271

faceman
Participant

The three parameter Weibull is the same as the two except it has a 3rd parameter (Threshold – symbol mu).  No defects happen before mu.  In a two parameter the defects can starts near 0.
Regards,
Bruce

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#118287

BTDT
Participant

Bernard:I see Weibull distributions whenever there is a time related metric. The distribution can be used to model the liklihood that something will occur (fail), given that it has survived to that time. The two parameters are scale and shape. The third parameter, threshold is the initial delay. It shifts the entire curve to the right.
If you are seeing it for the cycle time of the deformation process, the threshold parameter probably corresponds to your fixed setup time, while the rest of the distribution gives that range of execution times.
… or is the data some physical parameter?
BTDT

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