Reading Preestablished Control Limits

UCHART Statement

Reading Preestablished Control Limits

See SHWUCHR in the SAS/QC Sample Library

In the previous example, control limits were saved in a SAS data set named FABLIM. This example shows how these limits can be applied to defect counts for an additional 20 rolls of fabric, which are provided in the following data set:

   data fabric2;
      input roll defects @@;
      datalines;
   21  9    22  9    23 12    24  7    25 14
   26  5    27  4    28 13    29  6    30  7
   31 11    32 10    33  7    34 11    35  8
   36  8    37  3    38 10    39  9    40 13
   ;

The following statements create a u chart for the second group of rolls using the control limits in FABLIM:

   title 'u Chart for Fabric Defects';
   symbol v=dot c=vig;
   proc shewhart data=fabric2 limits=fablim;
      uchart defects*roll / subgroupn = 30
                            cframe    = steel
                            cinfill   = ligr
                            cconnect  = vig
                            coutfill  = yellow;
   run;

The chart is shown in Figure 41.5 and indicates that the process is in control.

Figure 41.5: A u Chart for Second Set of Fabric Rolls

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 DEFECTS
the value of _SUBGRP_ matches the subgroup-variable name ROLL

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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