Chapter Contents |
Previous |
Next |
RCHART Statement |
See SHWREX1 in the SAS/QC Sample Library |
This example demonstrates how to create R charts
with probability limits.
The following statements read the disk drive test times
from the data set DISKS (see
"Creating Range Charts from Raw Data" ) and create
the R chart shown in Output 39.1.1:
title 'Probability Limits for Disk Drive Test Times'; symbol v=dot c=rose; proc shewhart data=disks; rchart time*lot / alpha = .01 outlimits = dlimits cframe = vipb cinfill = ywh cconnect = rose; run;
The ALPHA= option specifies the probability () that a subgroup range exceeds its limits. Here, the limits are computed so that the probability that a range is less than the lower limit is ,and the probability that a range is greater than the upper limit is .This assumes that the measurements are normally distributed. The OUTLIMITS= option names an output data set that saves the probability limits. A listing of DLIMITS is shown in Output 39.1.2.
The variable _ALPHA_ saves the value of .Note that, in this case, the upper probability limit is equivalent to an upper limit.
Output 39.1.1: R Chart with Probability LimitsThe following statements apply the limits in DLIMITS to the times in the data set DISKS2 (see "Reading Preestablished Control Limits" ):
title 'Probability Limits Applied to Second Set of Test Times'; symbol v=dot c=rose; proc shewhart data=disks2 limits=dlimits; rchart time*lot / readalpha cframe = vipb cinfill = ywh cconnect = rose; run;
The READALPHA option^{*} specifies that the variable _ALPHA_, rather than the variable _SIGMAS_, is to be read from the LIMITS= data set. Thus the limits displayed in the chart, shown in Output 39.1.3, are probability limits.
Output 39.1.3: Reading Probability Limits from a LIMITS= Data Set
Chapter Contents |
Previous |
Next |
Top |
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.