# X bar chart and R chart

As the production manager for an electronic circuit company you have encountered the following situation.

Part 1

A process for producing electronic circuits has achieved very high yield levels. An average of only 10 defective parts per million is currently produced.

What are the upper and lower control limits for a sample size of 100?

Recompute the upper and lower control limits for a sample size of 10,000?

Which of these two sample sizes would you recommend? Explain.

Part 2

Management has reconsidered the method of quality control and has decided to use process control by variables instead of attributes. For variables control a circuit voltage will be measured based on a sample of only five circuits. The past average voltage for samples of size 5 has been 3.1 volts, and the range has been 1.2 volts.

What would the upper and lower control limits be for the resulting control charts (average and range)?

Five samples of voltage are taken with the results in the table below. What action should be taken if any?

Discuss the pros and cons of using this variables control chart versus the control chart discussed in the first part of the assignment. Which do you prefer?

Sample 1 2 3 4 5

x 3.6 3.3 2.6 3.9 3.4

R 2.0 2.6 0.7 2.1 2.3

The deliverable is an EXCEL FILE that answers the above with the various control charts etc.

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#### Solution Summary

The solution gives how to find the upper control limit and lower control limit of X bar chart and R chart.