Re: reliability calculation with Normdist?

Thank you. I dont understand the Weibul translation.l The Weibul in Excel
has Alpha, and Beta parameters. How do I get Alpha and Beta from the
Normdist knowing the mean and SD?.
"Jack Tomsky" <jtomsky@xxxxxxxxxxxxx> wrote in message
news:4065117.1206926796596.JavaMail.jakarta@xxxxxxxxxxxxxxxxxxxxxxxxx
If given MTBF and standard deviation can the
reliabilty be predicted at a
defined operational range using Excels
Normaldistribution?

say mtbf = 50, sd= 20, then plug in the operating
duration.
NORMDIST(operating duration, 50, 20, true).
Is that a way to calculate reliability at a specifed
duration?
thanks!





A more realist distribution for the time to failure would be either a
gamma or a Weibull distribution.

To find the two gamma parameters in terms of the specified mean and
standard deviation, set the mean and standard deviation of the gamma to
the given mean and standard deviation and simply solve for the two
parameters analytically in closed form. Then use one minus Excel's cdf
for the gamma.

To find the two Weibull parameters in terms of the specified mean and
standard deviation, set the mean and standard deviation of the Weibull to
the given mean and standard deviation and solve for the two parameters
numerically. Then the reliability is exp(-(OD/b)^p)

Jack


.

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