Moving Average Chart

If action and warning limits are added to a moving average chart, they should be plotted at 31+Jn and 2l+Jn units of standard deviation, respectively. 

Figure 6.7 Data shown on (a) a Shewhart chart and (b) a moving average chart (n =4).

Figure SAQ 6.2 (a) Shewhart chart with warning and action limits at 2 and 3 standard deviations, respectively, (b) Moving average chart (n = 5) with warning and action limits at 2 Jn and 3 Jn standard deviations, respectively, (c) CUSUM chart, (d) CUSUM chart with V-mask.

The EWMA Control Chart refers to the Exponentially Weighted Moving Average Chart. The common approach is plotting process data as a time series and... 

Figure 2. Shows 5-point moving average chart.

This pattern, then, is a blend of the weighting functions employed by the Shewhart Control Chart and the CUSUM Chart. We make use of all data points yet more emphasis is placed on the recent ones. Although the Stepwise SPC Chart is a combination of the Shewhart Control Chart and the CUSUM Chart, the Exponentially Weighted Moving Average Chart is a compromise of the two. Figure 6 illustrates the EWMA. 

Moving Average Chart IIIIIL EWMA Chart ii ... 

Crowder, S., A Simple Method for Studying Run Length Distributions of Exponentially Weighted Moving Average Charts, Technometrics, 29, 401-407 (1987). 

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