See SHWRCHR in the SAS/QC Sample LibraryIn 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
:
ods graphics on; title 'Range Chart for Disk Drive Test Times'; proc shewhart data=Disks2 limits=Disklim; rchart Time*Lot / odstitle=title; run;
The ODS GRAPHICS ON statement specified before the PROC SHEWHART statement enables ODS Graphics, so the R chart is created using ODS Graphics instead of traditional graphics. The chart is shown in Figure 17.76.
The LIMITS= option in the PROC SHEWHART statement specifies the data set containing the control limits. By default,[72] 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
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 17.28 and LIMITS= Data Set for details concerning the variables that you must provide.
[72] In SAS 6.09 and in earlier releases, it is also necessary to specify the READLIMITS option to read control limits from a LIMITS= data set.