BIT 3414 Lecture Notes - Lecture 5: Statistical Process Control, Control Chart, Walter A. Shewhart
7 Feb 2018
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Document Summary
Key tool is a control chart: periodically take a sample from a process, calculate a statistic of interest from the sample, plot the statistic on a control chart, determine if the process is in control, prevent quality problems. Signs of a process in control: no sample points outside limits, most points near process average, about equal number of points above and below center line, points appear randomly distributed (no discernible pattern) If the process is in control, the sampling distribution of the plotted statistic should be ~normal (and the empirical rule applies) This class will always set the control limits 3 from the process average. Assess the chart to determine if the variation present is inherent to the process or if it needs to be removed. Common causes of variation: ever-present factors that contribute to small, random shifts in output, difficult to track to a source, present even when process is in control.
