Quality and Reliability Methods - SAS

Chapter 6 Cumulative Sum Control Charts 103
Cumulative Sum (Cusum) Charts
• Specify hour as the Sample Label.
• Click the H radio button and enter 0.25 into the text box.
• Click Specify Stats to open the Known Statistics for CUSUM Chart tab.
• Set Target to the average weight of 8.1.
• Enter a Delta value of 1.
• Set Sigma to the standard deviation 0.05.
Alternatively, you can submit the following JSL script:
Control Chart(Sample Size( :hour), H(0.25), Show Limits Legend(0), Chart Col(
:weight, CUSUM(Two Sided(0), Target(8.1), Delta(1), Sigma(0.05))));
The resulting output should look like the picture in Figure 6.8.
Figure 6.8 One-Sided Cusum Chart for the Oil1 Cusum.jmp Data
Notice that the decision interval or horizontal line is set at the H-value entered (0.25). Also note that no
V-mask appears with One-Sided Cusum charts.
The Show Parameters option in the Cusum chart popup menu shows the Parameters report in Figure 6.9.
The parameters report summarizes the charting parameters from the Known Statistics for CUSUM Chart
tab on the Control Chart launch dialog. An additional chart option, Show ARL, adds the average run
length (ARL) information to the report. The average run length is the expected number of samples taken
before an out-of-control condition is signaled:
• ARL (Delta), sometimes denoted ARL1, is the average run length for detecting a shift the size of the
specified Delta
• ARL(0), sometimes denoted ARL0, is the in-control average run length for the specified parameters
(Montogomery (1985)).