Reading Preestablished Control Limits

[See SHWIR1 in the SAS/QC Sample Library]In the previous example, the OUTLIMITS= data set Jetlim saved control limits computed from the measurements in Jets. This example shows how these limits can be applied to data for an additional 20 jet engines provided in the following data set:

data Jets2;
   input Engine Diam @@;
   label Diam   = "Inner Diameter (cm)"
         Engine = "Engine Number";
datalines;
21 81.8  22 87.5  23 80.0  24 89.3  25 83.9
26 76.3  27 75.8  28 82.4  29 82.6  30 77.7
31 79.3  32 81.4  33 76.8  34 75.9  35 86.3
36 77.4  37 80.9  38 87.1  39 85.7  40 73.3
;
run;

The following statements create individual measurements and moving range charts for the data in Jets2 using the control limits in Jetlim:

options nogstyle;
title 'Individual Measurements and Moving Range Control Charts';
proc shewhart data=Jets2 limits=Jetlim;
   irchart Diam*Engine / cframe = vigb
                         cconnect = yellow
                         coutfill = red
                         cinfill = vlib;
run;
options gstyle;

The charts are shown in Figure 13.10.9. The NOGSTYLE system option causes ODS styles not to affect traditional graphics. Instead, the IRCHART statement options control the appearance of the graph. The GSTYLE system option restores the use of ODS styles for traditional graphics produced subsequently.

The LIMITS= option in the PROC SHEWHART statement specifies the data set containing the control limits. By default,¹ this information is read from the first observation in the LIMITS= data set for which

• the value of _VAR_ matches the process name Diam

• the value of _SUBGRP_ matches the subgroup-variable name Engine

The charts indicate that the process is in control, since all the individual measurements and moving ranges lie within their respective control limits.

In this example, the LIMITS= data set was created in a previous run of the SHEWHART procedure. You can also create a LIMITS= data set with the DATA step. See LIMITS= Data Set for details concerning the variables that you must provide.

Output 13.10.9 Charts for Second Set of Engine Noise Levels (Traditional Graphics with NOGSTYLE