Reading Preestablished Control Limits

XRCHART Statement

Reading Preestablished Control Limits

See SHWXR1 in the SAS/QC Sample Library

In the previous example, the OUTLIMITS= data set saved control limits computed from the measurements in WAFERS. This example shows how these limits can be applied to new data provided in the following data set:

   data wafers2;
      input batch @;
      do i=1 to 5;
         input diamtr @;
         output;
         end;
      drop i;
      datalines;
   26 34.99 34.99 35.00 34.99 35.00
   27 34.99 35.01 34.98 34.98 34.97
   28 35.00 34.99 34.99 34.99 35.01
   29 34.98 34.96 34.98 34.98 34.99
   30 34.98 35.00 34.98 34.98 34.99
   31 35.00 35.00 34.99 35.01 35.01
   32 35.00 34.99 34.98 34.98 35.00
   33 34.98 35.00 34.99 35.00 35.01
   34 35.00 34.97 35.00 34.99 35.01
   35 34.99 34.99 34.98 34.99 34.98
   36 35.01 34.98 34.99 34.99 35.00
   37 35.01 34.99 34.97 34.98 35.00
   38 34.98 34.99 35.00 34.98 35.00
   39 34.99 34.99 34.99 34.99 35.01
   40 34.99 35.01 35.00 35.01 34.99
   41 34.99 35.00 34.99 34.98 34.99
   42 35.00 34.99 34.98 34.99 35.00
   43 34.99 34.98 34.98 34.99 34.99
   44 35.00 35.00 34.98 35.00 34.99
   45 34.99 34.99 35.00 34.99 34.99
   ;

The following statements create $\bar{X}$ and R charts for the data in WAFERS2 using the control limits in WAFERLIM:

   title 'Mean and Range Charts for Diameters';
   symbol v=dot c=salmon;
   proc shewhart data=wafers2 limits=waferlim;
      xrchart diamtr*batch / cframe   = bigb
                             cinfill  = ywh
                             coutfill = ligr
                             cconnect = salmon;
   run;

The charts are shown in Figure 43.9.

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

the value of _VAR_ matches the process name DIAMTR
the value of _SUBGRP_ matches the subgroup-variable name BATCH

Figure 43.9: $\bar{X}$ and R Charts for Second Set of Wafer Data

Note that the mean diameter of the 29^th batch lies below the lower control limit in the $\bar{X}$ chart, signaling a special cause of variation.

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.

Chapter Contents
Previous
Next
Top