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Control Charts for Variables. Expected Outcomes. Know the three categories of variation and their sources. Understand the concept of the control chart method. Know the purpose of variable control charts.
Control charts help prevent overreactions to normal process variability while prompting quick responses to unusual variation. Control charts are also known as Shewhart charts. A stable process operates within an ordinary, expected range of variation.
decide which control chart for variables to use in a given situation; describe the procedure for constructing a control chart; construct and interpret the control chart for process mean(X-chart); S-chart); define the concepts of specification limits, natural tolerance limits and process capability. 2.2 CONTROL CHART TECHNIQUE .
Feb 18, 2013 · Variables control charts (those that measure variation on a continuous scale) are more sensitive to change than attribute control charts (those that measure variation on a discrete scale). Variables charts are useful for processes such as measuring tool wear.
Control charts for variables are of three types: Mean or Chart. Range or R chart. Standard deviation or σ chart. CONTROL CHART. Control charts for Range – R chart. R charts are used to control the variability in process. R charts are normally presented along with chart.
xand. R Charts. Equations 5-4 and 5-5 are trial control limits. Determined from m initial samples. Typically 20-25 subgroups of size n between 3 and 5. Any out-of-control points should be examined for assignable causes. If assignable causes are found, discard points from calculations and revise the trial control limits.
Shewhart Control Charts for variables. Let \ (w\) be a sample statistic that measures some continuously varying quality characteristic of interest (e.g., thickness), and suppose that the mean of \ (w\) is \ (\mu_w\), with a standard deviation of \ (\sigma_w\).
