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RCHART Statement |
See SHWRCHR in the SAS/QC Sample Library |
You can save the control limits for an R chart in a SAS data set; this enables you to apply the control limits to future data (see "Reading Preestablished Control Limits" ) or modify the limits with a DATA step program.
The following statements read measurements from the
data set DISKS (see
"Creating Range Charts from Raw Data" )
and save the control limits displayed in
Figure 39.2 in a data set named DISKLIM:
title 'Control Limits for Disk Times'; proc shewhart data=disks; rchart time*lot / outlimits = disklim nochart; run;
The data set DISKLIM contains one observation with the limits for process TIME. The variables _LCLR_ and _UCLR_ contain the lower and upper control limits, and the variable _R_ contains the central line. The value of _MEAN_ is an estimate of the process mean, and the value of _STDDEV_ is an estimate of the process standard deviation .The value of _LIMITN_ is the nominal sample size associated with the control limits, and the value of _SIGMAS_ is the multiple of associated with the control limits. The variables _VAR_ and _SUBGRP_ are bookkeeping variables that save the process and subgroup-variable. The variable _TYPE_ is a bookkeeping variable that indicates whether the values of _MEAN_ and _STDDEV_ are estimates or standard values. The variables _LCLX_ and _UCLX_, which contain the lower and upper control limits for subgroup means, are included so that the data set DISKLIM can be used to create an chart (see Chapter 43, "XRCHART Statement"). For more information, see "OUTLIMITS= Data Set" .
You can create an output data set containing both control limits
and summary statistics with the OUTTABLE= option, as illustrated
by the following statements:
title 'Summary Statistics and Control Limit Information'; proc shewhart data=disks; rchart time*lot / outtable=disktab nochart; run;
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This data set contains one observation for each subgroup
sample. The variables _SUBR_ and _SUBN_ contain
the subgroup ranges and subgroup sample sizes.
The variables _LCLR_ and _UCLR_ contain the lower
and upper control limits, and the variable _R_ contains
the central line.
The variables _VAR_ and BATCH contain the process name and
values of the subgroup-variable, respectively. For more
information, see "OUTTABLE= Data Set" .
An OUTTABLE= data set can be read later as a TABLE= data set.
For example, the following statements read DISKTAB and
display an R chart (not shown here) identical to
the chart in Figure 39.2:
title 'Range Chart for Disk Drive Test Times'; proc shewhart table=disktab; rchart time*lot; run;
Because the SHEWHART procedure simply displays the information
in a TABLE= data set,
you can use TABLE= data sets to create specialized control charts
(see Chapter 49, "Specialized Control Charts").
For more information, see "TABLE= Data Set" .
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