Reading Preestablished Control Limits

RCHART Statement

Reading Preestablished Control Limits

See SHWRCHR in the SAS/QC Sample Library

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

   data disks2;
      input lot @;
      do i=1 to 6;
         input time @;
         output;
         end;
      drop i;
   datalines;
   26 7.93 7.97 7.89 7.81 7.88 7.92
   27 7.86 7.91 7.87 7.89 7.83 7.87
   28 7.93 7.95 7.90 7.89 7.88 7.90
   29 7.97 8.00 7.86 7.89 7.84 7.78
   30 7.91 7.93 7.98 7.93 7.83 7.88
   31 7.85 7.94 7.88 7.98 7.96 7.84
   32 7.86 8.01 7.88 7.95 7.90 7.89
   33 7.87 7.93 7.96 7.89 7.81 8.00
   34 7.87 7.97 7.95 7.89 7.92 7.84
   35 7.92 7.97 7.90 7.88 7.89 7.86
   36 7.96 7.90 7.90 7.84 7.90 8.00
   37 7.92 7.90 7.98 7.92 7.94 7.94
   38 7.88 7.99 8.02 7.98 7.88 7.92
   39 7.89 7.91 7.92 7.90 7.94 7.94
   40 7.84 7.88 7.91 7.98 7.87 7.93
   41 7.91 7.87 7.96 7.91 7.89 7.92
   42 7.96 7.93 7.86 7.93 7.86 7.94
   43 7.84 7.82 7.87 7.91 7.91 8.01
   44 7.93 7.91 7.92 7.88 7.91 7.86
   45 7.95 7.92 7.93 7.90 7.86 8.00
   ;

The following statements create an R chart using the control limits in DISKLIM:

   title 'Range Chart for Disk Drive Test Times';
   symbol v=dot c=rose;
   proc shewhart table=disks2 limits=disklim;
      rchart time*lot / cframe   = vipb
                        cinfill  = ywh
                        cconnect = rose;
   run;

The chart is shown in Figure 39.8. 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 TIME
the value of _SUBGRP_ matches the subgroup-variable name LOT

Figure 39.8: R Chart for Second Set of Disk Drive Test Times

All the ranges lie within the control limits, indicating that the variability in disk drive performance is still in statistical control.

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 Example 39.2 and "LIMITS= Data Set" for details concerning the variables that you must provide.

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