Section 3 Control Charts
Lesson S03-13
Text: Section 3 page 75 and Section 9 pages 11 – 12
Duration: 10 minutes
Introduction to Exercise 6
a. It is wise to ignore the first chart signal and wait for another to be sure the process is out-of-control before reacting (true/false).
Solution/Discussion: Exercise 6 a
b. When should control limits be recomputed?
Solution/Discussion: Exercise 6 b
c. Provide an example (from your operation, if possible) where obtaining a rational sample may be problematic.
Solution/Discussion: Exercise 6 c
d. How does the subgroups size affect the sensitivity (ability to detect process changes) of an X̄ chart?
Solution/Discussion: Exercise 6 d
e. A beer bottler labels the product as a 12 fluid oz container. The filling process standard deviation (for volume) is 0.12 fluid oz. The fill volumes follow a normal distribution and the bottler decides to center the process at 12.36 to protect from “underfills.”
What is the sample size required to detect a shift of 0.18 fl oz with 80% probability (type II error is 0.20)?
Hint: Use MINITAB or the Excel worksheet Control Chart Sample Size.XLS
Solution/Discussion: Exercise 6 e
f. This is a continuation of the previous problem. Following a variation reduction effort, the standard deviation for the fill volume has been reduced from 0.12 to 0.08 fl oz.
What is the sample size required now to detect a shift of 0.18 fl oz with 80% probability (type II error is 0.20)?
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