u Chart VI

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Updated2024-11-20
6 minute(s) read

Computes points and limits for a u Chart - a control chart for number of non-conformities or defects per unit. Sample size in terms of number of units inspected n can be constant for all c or a constant value. Calculates both variable and constant chart limits. A range of indices for samples to be used and indices to ignore in the control calculation can also be specified. The actual number of samples used to calculate the control limits is supplied. FORMULAS: u-bar = · c / · n u(i) = c(i)/n(i) UCLu = u-bar + stderr mult x sqrt(u-bar/n(i)) CLu = u-bar LCLu = u-bar - stderr mult x sqrt(u-bar/n(i)) standard error = sqrt(u-bar/n(i))

Inputs/Outputs

chart limit src —

chart limit src specifies whether or not to use standard values for the chart limit calculations. If unwired this defaults to the most common case where the chart limits are calculated from the data in the input array(s). You do not have to wire this cluster unless you want the chart limits to be calculated from standard values. When using standard values, the center line for the control chart, u-bar, is set to u0.

source —

std u0 —

c:# defects/sample —

c:# defects/sample is the number of non-conformities or defects found for each number inspected.

n: sample size(variable) —

n: sample size (variable) is the number of units inspected for each value of c. Use this array if a variable number of units were inspected for each entry in c. The array length must be the same as the length of the array c.

n: sample size (constant) —

(U32) sample size - number of units inspected for each enty in c. Use this input if the same number of units were inspected for each entry in c. Otherwise, if you are providing an array for n, leave this input unwired.

std error multiplier (3) —

(DBL, default = 3.0). Ordinarily you would leave this unwired and the control chart limits are computed as +/- 3.0 standard errors.

index spec —

index spec is used to choose a range of samples in c to use for the control limit calculation. If you do not wire this cluster, all elements in c input array are included in the control limit calculation.

start index —

end index —

indices to ignore —

indices to ignore is the indices of samples to exclude from the control limit calculation. Excluding samples is useful for eliminating out of control points from the control limit calculation. By default, this is an empty array.

# samples in calc —

(I32) - the number of samples used in the control limits calculation.

u: average # defects/unit —

u: average # defects/unit is the number of defects divided by the number inspected. This is the average number of non-conformities or defects per unit inspected. This array is plotted on the u control chart.

UCLu —

LCLu —