16-8 ATTRIBUTE CONTROL CHARTS 629(times n) of the corresponding elements of a Uchart. The use of a Cchart avoids the fractions
that can occur in a Uchart.1 234567891011121314151617181920UCL = 3.3Sample numberDefects per unit,u240u = 1.6Figure 16-17 Uchart
of defects per unit on
printed circuit boards.16-24. Suppose the following fraction defective has been
found in successive samples of size 100 (read down):0.09 0.03 0.12
0.10 0.05 0.14
0.13 0.13 0.06
0.08 0.10 0.05
0.14 0.14 0.14
0.09 0.07 0.11
0.10 0.06 0.09
0.15 0.09 0.13
0.13 0.08 0.12
0.06 0.11 0.09(a) Using all the data, compute trial control limits for a
fraction-defective control chart, construct the chart, and
plot the data.
(b) Determine whether the process is in statistical control. If not,
assume assignable causes can be found and out-of-control
points eliminated. Revise the control limits.
16-25. The following represent the number of solder de-
fects observed on 24 samples of five printed circuit boards: 7,
6, 8, 10, 24, 6, 5, 4, 8, 11, 15, 8, 4, 16, 11, 12, 8, 6, 5, 9, 7, 14,
8, 21.
(a) Using all the data, compute trial control limits for a Ucon-
trol chart, construct the chart, and plot the data.
(b) Can we conclude that the process is in control using a U
chart? If not, assume assignable causes can be found, list
points and revise the control limits.
16-26. The following represent the number of defectsEXERCISES FOR SECTION 16-8
per 1000 feet in rubber-covered wire: 1, 1, 3, 7, 8, 10, 5, 13,
0, 19, 24, 6, 9, 11, 15, 8, 3, 6, 7, 4, 9, 20, 11, 7, 18, 10, 6, 4,
0, 9, 7, 3, 1, 8, 12. Do the data come from a controlled
process?
16-27. Consider the data in Exercise 16-25. Set up a Cchart
for this process. Compare it to the Uchart in Exercise 16-25.
Comment on your findings.
16-28. The following are the numbers of defective sol-
der joints found during successive samples of 500 solder
joints:Day No. of Defectives Day No. of Defectives
1 106 12 37
2 116 13 25
3 164 14 88
4 89 15 101
599 16 64
640 17 51
7 112 18 74
836 19 71
969 20 43
10 74 21 80
11 42(a) Using all the data, compute trial control limits for a
fraction-defective control chart, construct the chart, and
plot the data.
(b) Determine whether the process is in statistical control. If not,
assume assignable causes can be found and out-of-control
points eliminated. Revise the control limits.c 16 .qxd 5/8/02 9:58 PM Page 629 RK UL 6 RK UL 6:Desktop Folder: