![]() What it shows for the Mean value and Sigma value are the values calculated based on the current data. When you select the Simulate Data button in the XBar-R Chart-2 chart above, the dialog below appears: You can simulate this using the interactive chart above. ![]() When the process starts to go out of control, it should produce alarms when compared to the control limits calculated when the process was in control. Instead, as you move forward, you apply the previously calculated control limits to the new sampled data. Because once the process goes out of control, you will be incorporating these new, out of control values, into the control limit calculations, which will widen the control limits. What you don’t want to do is constantly recalculate control limits based on current data. The control limit lines and values displayed in the chart are a result these calculations. Therefore it is a suitable source of data to calculate the UCL, LCL and Target control limits. ![]() The initial chart represents a sample run where the process is considered to be in control. Where the constants D3 and D4 are tabulated for various sample sizes in the Table of XBar-R Chart Factors table below. Where the constant A2 is tabulated for subgroup sizes 2-8 in the Table of XBar-R Chart Factors table below.Ĭontrol Limits for the R (Range) – bottom chart You will find the chart listed under may different names, including: XBar-R, XBar and Range, \(\bar\\\) The XBar-R pair of charts are the most commonly used charts in SPC.
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