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Quality Control. COB 300 C - The Operations Dimension Busing. Causes of Variation. Random Causes difficult or expensive to control e.g., outside humidity, line voltage Assignable Causes easier to correct e.g., employee error, new materials. Comparing Process Variation to Tolerance Limits.
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Quality Control COB 300 C - The Operations Dimension Busing
Causes of Variation • Random Causes • difficult or expensive to control • e.g., outside humidity, line voltage • Assignable Causes • easier to correct • e.g., employee error, new materials
Control Charts • Variables - concentrates on mean for some measurable characteristic. • diameter • length • Attribute - data is based on counts or the number of times we observe a particular event. • proportion defective/non-defective • go/no go • proportion pass/fail
Control Limits - Variables Charts X-Bar Chart R Chart
Factors for Control Limits(Slide 1 of 2) Sample of Size n A D D 2 3 4 2 3 4 5 6 7 8 9 10 1.880 1.023 0.729 0.577 0.483 0.419 0.373 0.337 0.308 0 0 0 0 0 0.076 0.136 0.184 0.223 3.268 2.574 2.282 2.114 2.004 1.924 1.864 1.816 1.777
Warning Conditions • Two successive points near limit • Run of five above or below mean • Trend • Erratic behavior
Process Control for Attributes Proportion defective: Number of defects per unit: