SChart is an S chart using sample standard deviations to monitor the variability of a process. This is normally used with sample sizes greater than 10.

Namespace: Imsl.Chart2D.QC
Assembly: ImslCS (in ImslCS.dll) Version: 6.5.0.0

Syntax

C#
[SerializableAttribute]
public class SChart : ShewhartControlChart
Visual Basic (Declaration)
<SerializableAttribute> _
Public Class SChart _
	Inherits ShewhartControlChart
Visual C++
[SerializableAttribute]
public ref class SChart : public ShewhartControlChart

Remarks

The control limits are at

\bar{s} + k \frac{\bar{s}}{c_{4,n}}\sqrt{1-c_{4,n}^2}
where \bar{s} is the mean of the within sample standard deviations, n is the sample size, and k is the value of the "ControlLimit" attribute for the line. Additionally,
c_{4,n}=\sqrt{\frac{2}{n-1}}\frac{\Gamma(\frac{n}{2})}{\Gamma(\frac{n-1}{2})}
is a factor such that \bar{s}/c_{4,n} is an unbiased estimator of the within sample standard deviation. By default, the chart contains an upper control limit line with k=3, a lower control limit line with k=-3, and a central line equal to \bar{s}. Additional control limit lines can be added. The method AddWeco adds control limits with k = -2, -1, 1, 2.

Inheritance Hierarchy

See Also