Question

Assume you are working in a plant as a chemical engineer. One of your tasks is to monitor pH of a specific process. Each day, you record the pH of the process at three different time of the day. The data for the past few days is presented in the following table. we know that standard deviation of the pH of the process is 0.1. Based on the collected data, construct two control charts that monitor the average and variability of the pH of the process. Is the average and variability of the process in control?

Day.........................................Recorded pH
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Monday.........................7.67.........7.59.........7.07
Tuesday.........................7.64.........7.59.........7.27
Wednesday...................7.16.........7.84.........7.62
Thursday.......................7.20.........7.69.........7.30

1. Calculate the center line to control the average of pH of the process.

2. Calculate the average of ranges to control the variability of pH of the process.

3. Number of observation in each sample (n):

D4:

D3:

4. Upper and Lower Control Limit to control average of the pH of the process:

5. Upper and Lower Control Limit to control variability of the pH of the process:

Answer 1