Question

Solve using Minitab.

The table is observations on weekly operational downtime on a critical equipment (order read top to bottom and left to right). The target value for the mean is 25. (a) Estimate the process standard deviation. (b) Set up and apply a tabular cusum chart for this process, using standardized values h = 5 and k = ½. (c) Interpret the cusum chart.

24 22 27 27 25
27 23 20 28 29
24 28 20 29 21
20 20 27 18 27
21 19 19 25 27
27 31 20 28 26
24 25 19 24 25
27 23 31 25 24
28 23 21 21 23
25 22 19 28 29

(d) Plot the temperature data as an EWMA control chart using λ = 0.1 and L = 2.7. Interpret the EWMA control chart in comparison to the cusum chart.

Answer 1

ANSWER:

Given that,

Please note that answers are based on minitab output.

Part a

The estimated process standard deviation is given as 3.4.

Part b

For the standardized value h = 5 and k = 1/2 , the cusum chart by using Minitab for this process is given as below:

Part c

Interpretation:

The above chart shows that no any one point or observations is out of upper CUSUM and lower CUSUM, so we concluded that the given process is under statistically control.

Part d

Here, we have to construct EWMA control chart by using Minitab. The chart is given as below:

Lambda = 0.1 and L = 2.7

From this chart, it is observed that the process is in statistical control.