In: Statistics and Probability
The following represents the number of solder defects on 24 samples on ve printed circuit boards; 7,6,8,10,24,6,5,4,8,11,15,8,4,15,11,12,8,6,5,9,7,14,8,21.
(a) Using all the data, compute trial control limits for a U control chart, construct the chart and plot the data.
(b) Can we conclude that the process is in control using a U chart? If not, assume assignable causes can be found, list points and revise the control limits.
ANSWERS:
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Ans a)
Control limits for U chart is,
Upper control limits are = 0.729
Lower control limits are = 0.014
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Graph:
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Ans b)
The process is not in control.
One point more than 3.00 standard deviations from the
centerline.
Test Failed at points: 5, 24
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