Watson Wafers Ltd. Manufacture electronic components
Watson Wafers Ltd. Manufacture electronic components. For one of their
manufacturing processes, they have recorded some data that they wish to use
control charts to monitor. They wish to use an x-bar chart to see when their system
may be subject to problems, and need to calculate the control limits for the system
(both the UCL and the LCL).
The company operate a 6 hour working shift (without breaks), and following the start
of the shift a sample measure of the component produced by the process was taken
every 20 minutes. At each sample time 6 component readings were taken.
The company found that in their first shift the data recorded gave the following
values:
∑ = 280.2 and that ∑ s = 8.44
n 2 3 4 5 6 7 8 9 10 11
an 0.798 0.886 0.921 0.940 0.952 0.959 0.965 0.969 0.973 0.975
Table Q4a
Calculate the Upper and Lower Control Limits for the company using the appropriate
constant given in Table Q4a.
Show your workings and any equations used.
Comment upon the values of the constant in the table. (Maximum 100 words).
(5 marks)