vdoc

Chapter 19: B. Statistical Process Control 291
Continued
u Chart of Nonconformities
13
Sample count per unit
12
11
10
9
8
7
6
5
4
3 6 9 12 15 18 21 24 27 30
Sample
UCL = 12.124
u – = 8.267
LCL = 4.409
Figure 19.14 u chart of nonconformities for the data in Table 19.8.
To illustrate the construction of the u chart when the sample sizes vary, we
consider the following example.
EXAMPLE 19.11
Suppose that in Example 19.10, due to some administrative reasons, it was not possible
to examine five inspection units every day. In other words, the sample size varied and
the data obtained was as shown in Table 19.9. Construct and interpret a u chart for the
data in Table 19.9.
Solution:
Using the data in Table 19.9, we have
Part IV.B.4
33+ 40+ 38+ ... + 40 1162
u =
= = 922 . .
3+ 5+ 3+ ... + 3 126
Continued