Charts | Out-of-Control

Binomial Poisson Normal Charts Histograms Hypothesis Testing

  p Chart pn Chart u Chart c Chart X-Bar R X-Bar s I-MR / X-MR Out-of-Control

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Typical Out-of-Control Conditions / Patterns

• Points outside of limits (freaks)
• Less than 2/3 of all points in the middle 1/3 of control limit zone
• 7 consecutive point all above or below CL

• 8 consecutive points upward or downwards

• If any of the above 4 tests fail, process is out-of-control for Range. Investigate for special causes.
• If all 4 tests pass, process is in-control for Range. Interpret for control on X chart.
• If all 4 tests pass in X chart as well, then the process is in-control.

When Dealing with Control Charts

• What are the relationships between Control Limits and Specification Limits? Control Limits should be within the Specification Limits.
• Is it possible to have point within the Control Limits, but outside the Specification Limits? Yes, because the formula for creating Control Limits to not encompass the Specification Limits. For instance, the mean could be shifted.

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