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Control Charts

Control Charts. originally developed by Walter A. Shewhart. Control Charts. The control chart is a statistical quality control tool used in the monitoring variation in the characteristics of a product or service. Control Charts.

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Control Charts

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  1. Control Charts originally developed by Walter A. Shewhart

  2. Control Charts The control chart is a statistical quality control tool used in the monitoring variation in the characteristics of a product or service

  3. Control Charts The control chart focuses on the time dimension and the nature of the variability in the system.

  4. Control Charts The control chart may be used to study past performance and/or to evaluate present conditions.

  5. Control Charts Data collected from a control chart may form the basis for process improvement.

  6. Control Charts

  7. Control Charts • UCL =Process Average + 3 Standard Deviations • LCL = Process Average - 3 Standard Deviations X UCL + 3 Process Average - 3 LCL TIME Levine, Prentic-Hall

  8. Control Charts • Graph of sample data plotted over time Assignable Cause Variation UCL Process Average  Mean LCL Random Variation Levine, Prentice-Hall

  9. Control Charts X X X Special Cause Variation: two points outside control limit Common Cause Variation: no points outside control limit Downward Pattern: no points outside control limit; however, eight or more points in trend Levine, Prentice-Hall

  10. Control Charts • Attribute charts • Variables charts

  11. Control Charts Charts may be used for categoricalvariables. [i.e.: attributes]

  12. Control Charts Whenever a character of interest is measured on a nominative or an interval, ie: categorical, scale…an attributes control chart is used to monitor a process.

  13. Control Charts • Attributes Control Charts counts [c-chart] proportion [p-charts]

  14. Control Charts • Attributes Control Charts when sample size are not constant and/or are unknown use counts charts [c-charts]

  15. Control Charts

  16. Control Charts • Attributes Control Charts when sample size are constant and are known use proportion charts [p-charts]

  17. Control Charts

  18. Control Charts Charts may be used for interval or ratio data [i.e.: variables]

  19. Control Charts Whenever a character of interest is measured on an interval or a ratio scale, a variables control chart is used to monitor a process.

  20. Control Charts • Variables Control Charts Mean and Range charts [x-bar & R charts]

  21. Control Charts Variables control charts are typically used used in pairs. …… one chart monitors process average while the other monitors the variation in a process.

  22. Control Charts

  23. Control Charts

  24. Control Charts In conclusion: the control chart is a means of monitoring variation in the characteristics of a product or service

  25. Control Charts Know the assumptions … let the computer do the hard work.

  26. Control Charts Questions?

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