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Chapter 19: B. Statistical Process Control 273
Continued
X – chart
Sample mean
Sample standard
deviation
15.18
15.16
15.14
0.04
0.03
0.02
0.01
0.00
2 4 6 8 10 12 14 16 18 20 22 24
Sample
s chart
2 4 6 8 10 12 14 16 18 20 22 24
Sample
1
UCL = 15.18814
X – = 15.1628
LCL = 15.13746
UCL = 0.03527
s – = 0.01557
LCL = 0
Figure 19.9 The X – and S control chart for the ball bearing data in Table 19.3.
4. ATTRIBUTES CHARTS
Identify characteristics and uses of p, np, c,
and u charts. (Application)
Body of Knowledge IV.B.4
Part IV.B.4
As noted earlier in this chapter, quality characteristics are usually of two types,
called variables and attributes. In the previous section we studied control charts
for variables for detecting large process shifts. However, not all quality characteristics
can be measured numerically. For example, we may be interested in
finding whether the new car paint meets specifications in terms of shine, uniformity,
and scratches. Clearly, in this example we can’t quantify the shine, blemishes,
and scratches. In other words, we can not measure the shine, uniformity,
or the scratches numerically; consequently, to study the quality of paint on new
cars, we can not use control charts for variables. Sometimes, this type of situation
can arise when a quality characteristic is measurable, but because of cost,