You are here: NI Home > Support > Product Reference > Manuals > LabVIEW 8.6 Datalogging and Supervisory Control Module Help

Owning Palette: Control Charts VIs

Installed With: Statistical Process Control Toolkit

Computes points and limits for X-bar and s control charts. These are control charts for showing mean and sample standard deviation. Optionally, you can choose a range of indices for samples to use and indices of samples to ignore in the control limit calculation. The VI outputs the actual number of samples used to calculate the control limits. By default, control limits are calculated from the input samples. You can also calculate control limits from standard values by wiring the chart limit src input.

Details  

	chart limit src specifies whether or not to use standard values for the chart limit calculations. If unwired, this cluster defaults to the common case where the chart limits are calculated from the data in the input sample array. 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 X-bar control chart, X-bar-bar, is set to std mean, and the center line for the s control chart, s-bar, is set to std s0, or std sigma*c4. source selects one of three choices for source of chart limits calculation: 0 from data—(Default) chart limits are calculated from samples. 1 use std mean, s0—chart limits are calculated from standard mean and s0. 2 use std mean, sigma—chart limits are calculated from standard mean and sigma. std mean is the standard mean value to use in calculating chart limits from standard values. std s0/sigma specifies the standard s0 or standard sigma to use in calculating chart limits.
	samples X are the samples on which to compute control limits and points for the X-bar and s Chart. Each row is a sample with n observations were n is the number of columns in the 2D array. n is also known as the subgroup size. The minimum sample/subgroup size is 2.
	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 is the index of the first element of c to include in the control limit calculation. Default is 0 or index of the first sample in the c array. end index is the index of the last element of c to include in the control limit calculation. Default is 0 which selects the last sample in the c array.
	indices to ignore contains indices of samples to exclude from the control limit calculation, which is useful for eliminating out of control points from the control limit calculation. By default, this is an empty array.
	std error multiplier (3) is the multiplier to use for the upper and lower control limits. Normally you leave std error multiplier unwired, and the VI sets the control chart limits to ±3.0 standard errors. The default is 3.0.
	X-bar-bar is an estimate of the process mean based on the grand average of the samples included in the control limit calculation. If the control limits are calculated from standard values, this is set to the standard mean.
	X-bar is the mean of each input sample X. This is the array plotted on the X-bar control chart.
	X-bar chart limits contains the limits for the X-bar chart. UCLx is the upper control limit for the x chart. CLx is the center line for the X-bar control chart. Clx = x-bar-bar and is also the estimated process mean. LCLx is the lower control limit for the x chart. standard error is the standard error associated with the center line.
	s is the standard deviation of each input sample. This array is plotted on the s control chart.
	s chart limits contains the limits for the s chart. UCLs is the upper control limit for the s chart. CLs is the center line for the s control chart. CLs = s-bar. LCLs is the lower control limit for the s chart. standard error is the standard error associated with s-bar.
	s-bar/c4 is an estimate of the process sigma (standard deviation) based on the average standard deviation of the samples included in the control limit calculation.
	# samples in calc is the number of samples used in the control limits calculation. If the control limits are calculated from standard values, this is set to standard s0/c4 or sigma.

x-bar & S Chart Details

The control limit calculations for the chart limits are as follows.If standard values are used for the control limit calculations, then

(X-bar-bar) is set to std mean

s (s-bar) is set to std s0 or std sigma * c4, otherwise, X and s are calculated from the input samples as specified by the index spec and indices to ignore inputs.