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Comprehensive Guide to Control Charts: Understanding Options and Charting Methods

This chapter explores control charts in detail, addressing scenarios with insufficient samples or single samples. It covers various charting methods like Individuals and Moving Range, Moving Average and Moving Range, All Individual Values, Median and Range charts, and Run charts. Learn about variable sub-group sizes and pre-control charts to manage quality effectively.

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Comprehensive Guide to Control Charts: Understanding Options and Charting Methods

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  1. Other Variable Control Charts Chapter Seven Control Charts

  2. Other chart options • What happens when there is an insufficient number of sample measurements to create x-bar and r charts? • What happens when only one sample is taken? • What other charting methods are available? Control Charts

  3. Available chart options • Individual and Moving-Range • Moving-Average and Moving-Range • All Individual Values • Median and Range charts • Run charts • Variable sub-group size • Pre-control charts Control Charts

  4. Individuals and Moving-Range • Used when measurements are single values or when the number of products produced is too small to form traditional charts. • Moving ranges are calculated by measuring the value-to-value differences. • Interpretation is the same - check trends, runs, patterns, limits Control Charts

  5. Moving-average and Moving-range • Plot moving-average • replace oldest value with newest value • sample size n = number of selected values • Moving-averages smooth out short-term variation • Lags occur, charts are less sensitive to change Control Charts

  6. All individual values • Cluttered looking • Useful when examining individual variation Control Charts

  7. Median and Range charts • Median of the data is calculated and charted • Ease of calculation is a trade-off with some loss of sensitivity. • Constructed and interpreted like X-bar/R charts Control Charts

  8. Run charts • Used to monitor process changes associated with a particular characteristic over time. • Either variables or attribute data. • X-axis shows time. • Y-axis shows attribute/variable value. Control Charts

  9. Charts for variable sub-group size • Sub-group size coefficients must be recalculated • Each subgroup with a different sample size will have its own control limits plotted. • Con: lots of calculations! Control Charts

  10. Pre-control charts • Study and compare product produced with tolerance limits. Control Charts

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