Quality and Reliability Methods - SAS

32 Statistical Control Charts Chapter 2
The Control Chart Launch Dialog
Figure 2.6 Dialog Options for Variables Control Charts
XBar, R, and S
IR
EWMA
CUSUM
UWMA
Presummarize
Parameters
KSigma
• XBar charts menu selection gives XBar, R, and S checkboxes.
• The IR menu selection has checkbox options for the Individual Measurement, Moving Range, and
Median Moving Range charts.
• The uniformly weighted moving average (UWMA) and exponentially weighted moving average (EWMA)
selections are special charts for means.
• The CUSUM chart is a special chart for means or individual measurements.
• Presummarize allows you to specify information on pre-summarized statistics.
• P, NP, C, and U charts, Run Chart, and Levey-Jennings charts have no additional specifications.
The types of control charts are discussed in “Shewhart Control Charts” on page 69.
You specify computations for control limits by entering a value for k (K Sigma), or by entering a probability
for α(Alpha), or by retrieving a limits value from the process columns' properties or a previously created
Limits Table. Limits Tables are discussed in the section “Saving and Retrieving Limits” on page 45, later in
this chapter. There must be a specification of either K Sigma or Alpha. The dialog default for K Sigma is 3.
The KSigma parameter option allows specification of control limits in terms of a multiple of the sample
standard error. KSigma specifies control limits at k sample standard errors above and below the expected
value, which shows as the center line. To specify k, the number of sigmas, click the radio button for KSigma
and enter a positive k value into the text box. The usual choice for k is 3, which is three standard deviations.