Control Limits for t-charts

If there are no 0s in the data, the estimates of the shape and scale parameters are calculated from the data and used to obtain the percentiles of the Weibull distribution.

To estimate limits from the data:

If:

p1 = normalDist(-3) for Normal (0,1)

p2 = normalDist(0) for Normal (0,1)

p3 = normalDist(3) for Normal (0,1)

Then:

CL = Weibull Quantile (p2, β) * α

UCL = Weibull Quantile (p1, β) * α

LCL = Weibull Quantile (p3, β) * α

where:

β is the shape parameter and α is the scale parameter for the Weibull Quantile function. For more information about the Weibull Quantile function, see Help > Scripting Index.