Reading Preestablished Control Limits

NPCHART Statement

Reading Preestablished Control Limits

See SHWNP1 in the SAS/QC Sample Library

In the previous example, the OUTLIMITS= data set CIRLIM saved control limits computed from the data in CIRCUITS. This example shows how these limits can be applied to new data provided in the following data set:

   data circuit2;
      input batch fail @@;
   datalines;
   31  12   32   9   33  16    34   9
   35   3   36   8   37  20    38   4
   39   8   40   6   41  12    42  16
   43   9   44   2   45  10    46   8
   47  14   48  10   49  11    50   9
   ;

The following statements create an np chart for the data in CIRCUIT2 using the control limits in CIRLIM:

   title 'np Chart for the Proportion of Failing Circuits';
   symbol v=dot c=yellow;
   proc shewhart data=circuit2 limits=cirlim;
      npchart fail*batch / subgroupn = 500
                           cframe    = vibg
                           cinfill   = vlibg
                           coutfill  = salmon
                           cconnect  = yellow;
   run;

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 name FAIL
the value of _SUBGRP_ matches the subgroup-variable name BATCH

The resulting np chart is shown in Figure 37.8.

Figure 37.8: An np Chart for Second Set of Circuit Failures

The number of nonconforming items in the 37^th batch exceeds the upper control limit, signaling that the process is out of 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 37.4 for an example. See "LIMITS= Data Set" for details concerning the variables that you must provide.

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