Q6. A quality analyst took the followingsamples as a pilot study to construct the mean and range charts.The data below shows the weight in ounces. Construct the mean andrange charts showing all control (action) –upper and lower limits,and warning upper and lower limits.
Sample Number | Item1 | Item2 | Item3 | Item4 |
Sample 1 | 11.9 | 12.5 | 12.4 | 12.7 |
Sample 2 | 12.5 | 12.5 | 12.4 | 12.8 |
Sample 3 | 12.2 | 12.8 | 12.7 | 12 |
Sample 4 | 12.3 | 12.4 | 12.8 | 12.4 |
Sample 5 | 12.1 | 12.8 | 12.4 | 11.9 |
Sample 6 | 12.6 | 12.4 | 12.1 | 12.3 |
The following day, the analyst took another 6 samples to checkif the process under control or not. Theses samples are asfollows:
Sample Number | Item1 | Item2 | Item3 | Item4 |
Sample 1 | 11.9 | 11.5 | 12.4 | 12.3 |
Sample 2 | 12.5 | 11.5 | 13.4 | 11.8 |
Sample 3 | 12.2 | 11.8 | 11.7 | 12 |
Sample 4 | 14.3 | 11.4 | 11.8 | 13.4 |
Sample 5 | 15.1 | 11.8 | 12.4 | 10.9 |
Sample 6 | 11.6 | 10.4 | 10.1 | 15.3 |
Is the process under control? Why? What actions shouldyou take?
Factors for calculating control limits for control charts
For MEANS
Sample size (n) | Constant (dn) | Factors for warning limits 1.96/dn?n | Factors for action limits 3.09?n |
2 | 1.128 | 1.23 | 1.94 |
3 | 1.693 | 0.67 | 1.05 |
4 | 2.059 | 0.48 | 0.75 |
5 | 2.326 | 0.38 | 0.59 |
6 | 2.334 | 0.32 | 0.50 |
7 | 2.704 | 0.27 | 0.43 |
8 | 2.847 | 0.24 | 0.38 |
9 | 2.970 | 0.22 | 0.35 |
10 | 3.078 | 0.20 | 0.32 |
Factors for calculating control limits for control charts
For RANGES
Sample size | Upper warning limit | Lower warning limit | Upper action limit | Lower action limit |
2 | 2.81 | 0.04 | 4.12 | 0.00 |
3 | 2.17 | 0.18 | 2.98 | 0.04 |
4 | 1.93 | 0.29 | 2.57 | 0.10 |
5 | 1.81 | 0.37 | 2.34 | 0.16 |
6 | 1.72 | 0.42 | 2.21 | 0.21 |
7 | 1.66 | 0.46 | 2.11 | 0.26 |
8 | 1.62 | 0.50 | 2.04 | 0.29 |
9 | 1.58 | 0.52 | 1.99 | 0.32 |
10 | 1.56 | 0.54 | 1.94 | 0.35 |