Reading Preestablished Control Limits

MRCHART Statement

Reading Preestablished Control Limits

See SHWMR1 in the SAS/QC Sample Library

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

   data detergt2;
      input lot @;
      do i=1 to 5;
         input weight @;
         output;
         end;
      drop i;
      datalines;
   29 16.66 27.49 18.87 22.53 24.72
   30 23.74 23.67 23.64 20.26 22.09
   31 24.56 24.82 23.92 26.67 21.38
   32 25.89 28.73 29.21 25.38 23.47
   33 23.32 21.61 30.75 23.13 23.82
   34 23.04 22.65 24.96 19.64 26.84
   35 24.01 24.38 24.86 26.50 24.37
   36 26.43 27.36 28.74 26.74 26.27
   37 21.41 22.24 25.34 20.59 27.51
   38 22.62 20.81 22.64 30.15 25.32
   39 26.86 28.14 24.06 27.35 22.49
   40 23.03 23.83 25.59 19.85 22.33
   41 23.19 23.63 23.00 21.46 27.57
   42 27.38 23.18 24.99 24.81 28.82
   43 26.60 26.58 20.26 26.27 24.96
   44 26.22 23.28 24.15 24.06 28.23
   45 25.90 22.88 25.55 24.50 19.95
   46 16.66 27.49 18.87 22.53 24.72
   47 23.74 23.67 23.64 20.26 22.09
   48 24.56 24.82 23.92 26.67 21.38
   49 25.89 28.73 29.21 25.38 23.47
   50 23.32 21.61 30.75 23.13 23.82
   ;

The following statements create median and range charts for the data in DETERGT2 using the control limits in DETLIM:

   title 'Median and Range Charts for Weights';
   symbol v=dot c=rose;
   proc shewhart data=detergt2 limits=detlim;
      mrchart weight*lot / cframe   = vipb
                           cinfill  = ywh
                           cconnect = rose
                           coutfill = salmon;
   run;

The charts are shown in Figure 36.8. 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 WEIGHT
the value of _SUBGRP_ matches the subgroup-variable name LOT

Figure 36.8: Median and Range Charts for Second Set of Detergent Box Weights

The charts indicate that the process is in control, since all the medians and ranges lie within the 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.

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