Quality and Reliability Methods - SAS

56 Introduction to Control Charts Chapter 3
Control Charts in JMP
Figure 3.2 Parts of a Basic Control Chart
out-of-control point
upper control limit
centerline
lower control limit
Note the following about control charts:
• Each point plotted on the chart represents an individual process measurement or summary statistic. In
this example, the points represent the average for a sample of measurements.
• The X axis of the control chart is time ordered. Observing the process over time is important in assessing
if the process is changing.
• The two red lines are the upper and lower control limits. If the process is exhibiting only routine
variation, then all the points should fall randomly in that range. In this example, one measurement is
above the upper control limit. This is evidence that the measurement could have been influenced by a
special cause, or is possibly a defect.
• The green line is the center line, or the average of the data. Measurements should appear equally on both
sides of the center line. If not so, this is possible evidence that the process average is changing.
When a control chart signals abnormal variation, action should be taken to return the process to a state of
statistical control if the process degraded. If the abnormal variation indicates an improvement in the process,
the causes of the variation should be studied and implemented.
Control Charts in JMP
JMP 10 introduces a shift in the approach to control charts. We are moving toward an all-in-one, interactive
workspace called Control Chart Builder. Control Chart Builder can be used to create several types of control
charts, and is intended to be an interactive tool for problem solving and process analysis.
To use Control Chart Builder, you do not need to know the name of a particular chart beforehand. When
you drag a data column to the workspace, Control Chart Builder creates an appropriate chart based on the
data type and sample size. Once the basic chart is created, use the right-click menu to:
• change the statistic on the chart
• format the chart
• add additional charts