What do you understand by quality control by attributes and quality control by variables? 5
- Where do you need a large sample size in the above and why? 5
- Four batches of products are inspected at 90 minute intervals and their percentage difference in weights from the nominal are given below:
Percentage difference on weights in sample
|
Batch – 1
|
Batch – 2
|
Batch – 3
|
Batch – 4
|
|
1.2
|
0.6
|
0.6
|
2.1
|
|
1.8
|
0.3
|
1.5
|
0.6
|
|
1.5
|
0.3
|
1.0
|
0.6
|
|
0.9
|
0.0
|
0.0
|
2.7
|
|
0.3
|
0.6
|
1.9
|
2.7
|
Assume that normal process average variation is 0.9% and process standard deviation is 0.5%, range U.C.L. is 5 times S.D. Plot $\overbar{X}$, R chart indicating the various control limits. Is the process under control?