IMSL C# Chart Guide: ShewhartControlChart and ControlLimit

IMSL C# Programmer’s Guide

Quality Control and Improvement Charts >> ShewhartControlChart and ControlLimit

ShewhartControlChart and ControlLimit

The ShewhartControlChart class is primarily used as the base class of other control chart classes. It provides the common functionality for the control charts.

For example, the default IMSL.NET control charts include a center line and an upper and lower control limits at plus or minus three standard deviations from the center line. The Western Electric Company Rules (or WECO) are control limits at plus or minus one, two, and three standard deviations from the mean. They can be added using the method AddWecoLimits in the ShewhartControlChart class.

The ShewhartControlChart uses the ControlLimit class for the upper and lower control limits and for the center line. Additional control limits, such as the WECO limits, can be added to a ShewhartControlChart. The line attributes can be used with ControlLimit to modify the drawing of each control limit.

The ShewhartControlChart class can be used directly when the statistics are computed by the user. In this example, data from Montgomery, Douglas C., Introduction to Statistical Quality Control, 4th Ed,., 2001, New York: John Wiley and Sons, p. 406 is plotted. The code explicitly sets the lower control limit to 7 and the upper control limit to 13.

Further citations throughout this chapter for data plotted from Montgomery appear as parenthetical citations, e.g. (Montgomery 406).

(Download Code)

using Imsl.Chart2D;
using Imsl.Chart2D.QC;

public class SampleShewhart : FrameChart {
    static double[] data = {
        9.45, 7.99, 9.29, 11.66, 12.16, 10.18, 8.04, 11.46, 9.20, 10.34, 9.03,
        11.47, 10.51, 9.40, 10.08, 9.37, 10.62, 10.31, 8.52, 10.84, 10.90,
        9.33, 12.29, 11.50, 10.60, 11.08, 10.38, 11.62, 11.31, 10.52
    };

    public SampleShewhart() {
        Chart chart = this.Chart;
        AxisXY axis = new AxisXY(chart);
        ShewhartControlChart xbars = new ShewhartControlChart(axis);
        xbars.SetData(data);
        xbars.AddLowerControlLimit().SetValue(7);
        xbars.AddCenterLine().SetValue(10);
        xbars.AddUpperControlLimit().SetValue(13);
    }


    public static void Main(string[] argv) {
        System.Windows.Forms.Application.Run(new SampleShewhart());
    }
}