Note: See Mean and Standard Deviation Charts Examples in the SAS/QC Sample Library.
You can save the control limits for and s charts 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 Turbine
(see Creating Charts for Means and Standard Deviations from Raw Data) and save the control limits displayed in Figure 17.115 in a data set named Turblim
:
proc shewhart data=Turbine; xschart KWatts*Day / outlimits=Turblim nochart; run;
The OUTLIMITS= option names the data set containing the control limits, and the NOCHART option suppresses the display of the
charts. The data set Turblim
is listed in Figure 17.119.
The data set Turblim
contains one observation with the limits for process KWatts
. The variables _LCLX_
and _UCLX_
contain the lower and upper control limits for the chart, and the variables _LCLS_
and _UCLS_
contain the lower and upper control limits for the s chart. The variable _MEAN_
contains the central line for the chart, and the variable _S_
contains the central line for the s chart. 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. 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:
proc shewhart data=Turbine; xschart KWatts*Day / outtable=Turbtab nochart; run;
The data set Turbtab
is listed in Figure 17.120.
Figure 17.120: The OUTTABLE= Data Set Turbtab
Summary Statistics and Control Limit Information |
_VAR_ | Day | _SIGMAS_ | _LIMITN_ | _SUBN_ | _LCLX_ | _SUBX_ | _MEAN_ | _UCLX_ | _STDDEV_ | _EXLIM_ | _LCLS_ | _SUBS_ | _S_ | _UCLS_ | _EXLIMS_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
KWatts | 04JUL | 3 | 20 | 20 | 3351.92 | 3487.40 | 3485.41 | 3618.90 | 198.996 | 100.207 | 220.260 | 196.396 | 292.584 | ||
KWatts | 05JUL | 3 | 20 | 20 | 3351.92 | 3471.65 | 3485.41 | 3618.90 | 198.996 | 100.207 | 210.427 | 196.396 | 292.584 | ||
KWatts | 06JUL | 3 | 20 | 20 | 3351.92 | 3488.30 | 3485.41 | 3618.90 | 198.996 | 100.207 | 147.025 | 196.396 | 292.584 | ||
KWatts | 07JUL | 3 | 20 | 20 | 3351.92 | 3434.20 | 3485.41 | 3618.90 | 198.996 | 100.207 | 157.637 | 196.396 | 292.584 | ||
KWatts | 08JUL | 3 | 20 | 20 | 3351.92 | 3475.80 | 3485.41 | 3618.90 | 198.996 | 100.207 | 258.949 | 196.396 | 292.584 | ||
KWatts | 09JUL | 3 | 20 | 20 | 3351.92 | 3518.10 | 3485.41 | 3618.90 | 198.996 | 100.207 | 211.566 | 196.396 | 292.584 | ||
KWatts | 10JUL | 3 | 20 | 20 | 3351.92 | 3492.65 | 3485.41 | 3618.90 | 198.996 | 100.207 | 193.779 | 196.396 | 292.584 | ||
KWatts | 11JUL | 3 | 20 | 20 | 3351.92 | 3496.40 | 3485.41 | 3618.90 | 198.996 | 100.207 | 212.024 | 196.396 | 292.584 | ||
KWatts | 12JUL | 3 | 20 | 20 | 3351.92 | 3398.50 | 3485.41 | 3618.90 | 198.996 | 100.207 | 199.201 | 196.396 | 292.584 | ||
KWatts | 13JUL | 3 | 20 | 20 | 3351.92 | 3456.05 | 3485.41 | 3618.90 | 198.996 | 100.207 | 173.455 | 196.396 | 292.584 | ||
KWatts | 14JUL | 3 | 20 | 20 | 3351.92 | 3493.60 | 3485.41 | 3618.90 | 198.996 | 100.207 | 187.465 | 196.396 | 292.584 | ||
KWatts | 15JUL | 3 | 20 | 20 | 3351.92 | 3563.30 | 3485.41 | 3618.90 | 198.996 | 100.207 | 205.472 | 196.396 | 292.584 | ||
KWatts | 16JUL | 3 | 20 | 20 | 3351.92 | 3519.05 | 3485.41 | 3618.90 | 198.996 | 100.207 | 173.676 | 196.396 | 292.584 | ||
KWatts | 17JUL | 3 | 20 | 20 | 3351.92 | 3474.20 | 3485.41 | 3618.90 | 198.996 | 100.207 | 200.576 | 196.396 | 292.584 | ||
KWatts | 18JUL | 3 | 20 | 20 | 3351.92 | 3443.60 | 3485.41 | 3618.90 | 198.996 | 100.207 | 222.084 | 196.396 | 292.584 | ||
KWatts | 19JUL | 3 | 20 | 20 | 3351.92 | 3586.35 | 3485.41 | 3618.90 | 198.996 | 100.207 | 185.724 | 196.396 | 292.584 | ||
KWatts | 20JUL | 3 | 20 | 20 | 3351.92 | 3486.45 | 3485.41 | 3618.90 | 198.996 | 100.207 | 223.474 | 196.396 | 292.584 | ||
KWatts | 21JUL | 3 | 20 | 20 | 3351.92 | 3492.90 | 3485.41 | 3618.90 | 198.996 | 100.207 | 145.267 | 196.396 | 292.584 | ||
KWatts | 22JUL | 3 | 20 | 20 | 3351.92 | 3432.80 | 3485.41 | 3618.90 | 198.996 | 100.207 | 190.994 | 196.396 | 292.584 | ||
KWatts | 23JUL | 3 | 20 | 20 | 3351.92 | 3496.90 | 3485.41 | 3618.90 | 198.996 | 100.207 | 208.858 | 196.396 | 292.584 |
The data set Turbtab
contains one observation for each subgroup sample. The variables _SUBX_
, _SUBS_
, and _SUBN_
contain the subgroup means, subgroup standard deviations, and subgroup sample sizes. The variables _LCLX_
and _UCLX_
contain the lower and upper control limits for the chart. The variables _LCLS_
and _UCLS_
contain the lower and upper control limits for the s chart. The variable _MEAN_
contains the central line for the chart. The variable _S_
contains the central line for the s chart. The variables _VAR_
and Batch
contain the process name and values of the subgroup-variable, respectively. For more information, see OUTTABLE= Data Set.
A data set created with the OUTTABLE= option can be read later as a TABLE= data set. For example, the following statements
read Turbtab
and display charts (not shown here) identical to those in Figure 17.115:
title 'Mean and Standard Deviation Charts for Power Output'; proc shewhart table=Turbtab; xschart KWatts*Day; 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 Specialized Control Charts: SHEWHART Procedure). For more information, see TABLE= Data Set.