See SHWXR1 in the SAS/QC Sample LibraryYou can save the control limits for and R 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 `Wafers`

(see Creating Charts for Means and Ranges from Raw Data) and save the control limits displayed in Figure 17.105 in `Waferlim`

:

proc shewhart data=Wafers; xrchart Diameter*Batch / outlimits = Waferlim 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 `Waferlim`

is listed in Figure 17.109.

Figure 17.109: The Data Set `Waferlim`

Containing Control Limit Information

Control Limits for Wafer Diameters |

_VAR_ | _SUBGRP_ | _TYPE_ | _LIMITN_ | _ALPHA_ | _SIGMAS_ | _LCLX_ | _MEAN_ | _UCLX_ | _LCLR_ | _R_ | _UCLR_ | _STDDEV_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|

Diameter | Batch | ESTIMATE | 5 | .002699796 | 3 | 34.9823 | 34.9950 | 35.0077 | 0 | 0.022 | 0.046519 | .009458586 |

The data set `Waferlim`

contains one observation with the limits for *process* `Diameter`

. The variables `_LCLX_`

and `_UCLX_`

contain the lower and upper control limits for the chart. The variables `_LCLR_`

and `_UCLR_`

contain the lower and upper control limits for the R chart. The variable `_MEAN_`

contains the central line for the chart, and the variable `_R_`

contains the central line for the R 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* names. The variable `_TYPE_`

is a bookkeeping variable that indicates whether the values of `_MEAN_`

and `_STDDEV_`

are estimates or standard values.

You can save process capability indices in an OUTLIMITS= data set if you provide specification limits with the LSL= and USL= options. This is illustrated by the following statements:

proc shewhart data=Wafers; xrchart Diameter*Batch / outlimits = Waferlim2 usl = 35.03 lsl = 34.97 nochart; run;

The data set `Waferlim2`

is listed in Figure 17.110.

Figure 17.110: The Data Set `Waferlim2`

Containing Process Capability Indices

Control Limits and Capability Indices |

_VAR_ | _SUBGRP_ | _TYPE_ | _LIMITN_ | _ALPHA_ | _SIGMAS_ | _LCLX_ | _MEAN_ | _UCLX_ | _LCLR_ | _R_ | _UCLR_ | _STDDEV_ | _LSL_ | _USL_ | _CP_ | _CPL_ | _CPU_ | _CPK_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Diameter | Batch | ESTIMATE | 5 | .002699796 | 3 | 34.9823 | 34.9950 | 35.0077 | 0 | 0.022 | 0.046519 | .009458586 | 34.97 | 35.03 | 1.05724 | 0.87962 | 1.23486 | 0.87962 |

The variables `_CP_`

, `_CPL_`

, `_CPU_`

, and `_CPK_`

contain the process capability indices. It is reasonable to compute capability indices, since Figure 17.105 indicates that the wafer process is in statistical control. However, it is recommended that you also check for normality
of the data. You can use the CAPABILITY procedure for this purpose.

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=Wafers; xrchart Diameter*Batch / outtable=Wafertab nochart; run;

The data set `Wafertab`

is listed in Figure 17.111.

Figure 17.111: The Data Set `Wafertab`

Summary Statistics and Control Limit Information |

_VAR_ | Batch | _SIGMAS_ | _LIMITN_ | _SUBN_ | _LCLX_ | _SUBX_ | _MEAN_ | _UCLX_ | _STDDEV_ | _EXLIM_ | _LCLR_ | _SUBR_ | _R_ | _UCLR_ | _EXLIMR_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Diameter | 1 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 2 | 3 | 5 | 5 | 34.9823 | 34.994 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 3 | 3 | 5 | 5 | 34.9823 | 34.998 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 | ||

Diameter | 4 | 3 | 5 | 5 | 34.9823 | 34.998 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 5 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 6 | 3 | 5 | 5 | 34.9823 | 34.996 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 | ||

Diameter | 7 | 3 | 5 | 5 | 34.9823 | 34.996 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 8 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 9 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 10 | 3 | 5 | 5 | 34.9823 | 35.000 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 11 | 3 | 5 | 5 | 34.9823 | 34.996 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 12 | 3 | 5 | 5 | 34.9823 | 34.994 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 13 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 14 | 3 | 5 | 5 | 34.9823 | 34.998 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 15 | 3 | 5 | 5 | 34.9823 | 34.988 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 16 | 3 | 5 | 5 | 34.9823 | 35.000 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 17 | 3 | 5 | 5 | 34.9823 | 34.984 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 | ||

Diameter | 18 | 3 | 5 | 5 | 34.9823 | 35.002 | 34.9950 | 35.0077 | .009458586 | 0 | 0.04 | 0.022 | 0.046519 | ||

Diameter | 19 | 3 | 5 | 5 | 34.9823 | 34.988 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 20 | 3 | 5 | 5 | 34.9823 | 34.994 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 | ||

Diameter | 21 | 3 | 5 | 5 | 34.9823 | 34.992 | 34.9950 | 35.0077 | .009458586 | 0 | 0.02 | 0.022 | 0.046519 | ||

Diameter | 22 | 3 | 5 | 5 | 34.9823 | 35.002 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 | ||

Diameter | 23 | 3 | 5 | 5 | 34.9823 | 35.004 | 34.9950 | 35.0077 | .009458586 | 0 | 0.04 | 0.022 | 0.046519 | ||

Diameter | 24 | 3 | 5 | 5 | 34.9823 | 34.996 | 34.9950 | 35.0077 | .009458586 | 0 | 0.03 | 0.022 | 0.046519 | ||

Diameter | 25 | 3 | 5 | 5 | 34.9823 | 34.994 | 34.9950 | 35.0077 | .009458586 | 0 | 0.01 | 0.022 | 0.046519 |

This data set contains one observation for each subgroup sample. The variables `_SUBX_`

, `_SUBR_`

, and `_SUBN_`

contain the subgroup means, subgroup ranges, and subgroup sample sizes. The variables `_LCLX_`

and `_UCLX_`

contain the lower and upper control limits for the chart. The variables `_LCLR_`

and `_UCLR_`

contain the lower and upper control limits for the R chart. The variable `_MEAN_`

contains the central line of the chart, and the variable `_R_`

contains the central line of the R chart. 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 `Wafertab`

and display and R charts identical to those in Figure 17.105:

title 'Mean and Range Charts for Diameters'; proc shewhart table=Wafertab; xrchart Diameter*Batch; run;

Because the SHEWHART procedure simply displays the information read from 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.