Trying to Create Cusum Charts in Excel?
QI Macros can create cusum charts for you!
Draw a CUSUM Chart using QI Macros:
- Select your data.
- Select Control Charts (SPC) > Special> CUSUM from QI Macros menu.
- QI Macros will do the math and draw the graph for you.
Cumulative Sum Charts Can Detect Small Shifts in a Process
Cusum charts can detect process shifts more rapidly than the XmR or XbarR. If a trend develops, it's evidence that the process has shifted. In addition to a Cusum chart, you might consider an EWMA chart.
Example of a Cusum Chart Created by QI Macros Add-in for Excel
QI Macros also contains a ready made cusum chart template.
A Cusum Chart consists of:
- A target which is either provided by you or calculated as the mean of your data.
- Upper Cusum Limit and Lower Cusum Limit lines.
- C+ and C- lines which represent the cumulative sum of deviations of successive sample means from a target. Use these lines to determine if your process is shifting.
Default values calculated in the Cusum Chart:
NOTE: Using h=4 or h=5 and k=.5 will generally provide a cusum that has good ARL properties (per Montgomery SPC 4th ed.)
k (slack) = 1/2 of your StDev
(this is an estimated value, but can be changed)
FIR (Fast Initial Response) = 0
(This feature can be used to set an initial "head start" value to improve detection of an out-of-control condition at the start of the chart. If the process is in control, this initial head start has little effect; if the process is out of control, a signal will be given faster with a non-zero value than with a zero value)
h (threshold value or decision interval) = 4
(this determines how many StDev from the mean the Cusum Limits are set)
Compare a Cusum Chart with an EWMA Chart
Compare a Cusum Chart with an Individual Moving Range Chart
Notice how the Cusum chart more quickly and clearly identifies the process shift.
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QI Macros Draws These Charts Too!