About XBar charts

An XBar chart shows changes in the mean value of a process. XBar is the sample mean (or average). An XBar chart is used for measurable characteristics and shows any changes in the mean value of a process. (See iMonitor Designer for details about using iMonitor Designer.)

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XBar-R charts

An XBar-R chart plots the average of individual values in a subgroup. These charts are typically used to plot a subgroup mean for smaller subgroups and the range of individual values for a single characteristic. Use an XBar-R chart when the sample part size is between 2 and 9 (typically 3 or 5). This chart type is often used when at least a few parts are made every hour. 

The XBar-R control chart shows both the mean value (XBar) and the range (R) of a sample. This is the most common type of control chart using indiscrete or continuous values.The XBar portion of the chart shows any changes in the mean value of the process while the R portion shows any changes in the dispersion of the process. This chart is particularly useful because it shows changes in mean value and dispersion of the process at the same time, making it a very effective method for checking abnormalities in the process.

• The XBar part of the chart shows any changes in the mean value of a process

• The R part of the chart shows any changes in the dispersion of the process.

XBar-R charts are very useful because they show changes in both the mean value and the dispersion of a process at the same time, making it a very effective way to check for abnormalities in a process.

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XBar-S charts

XBar-S charts are identical to XBar-R charts except that the R (range) is replaced by an S (standard deviation).

An XBar-S chart plots the average and the sample standard deviation of individual values in a subgroup. These charts are typically used to plot the subgroup mean for a larger subgroup and the standard deviation. Use an XBar-S chart when your sample size is 10 or more (n≥10) and a lot of data is readily available, for example on high-speed production lines where many measurements can be gathered quickly.

An XBar-S chart shows both the mean value (XBar) chart and the standard deviation (S) chart. 

Create XBar-R and XBar-S charts in iMonitor Designer

You can create SPC XBar-R and XBar-S charts in iMonitor Designer to display in real-time dashboards. When you select the SPC (Statistical Process Control) category in the lower-left of the iMonitor Designer window, the Toolbox area shows options for creating XBar-R and XBar-S charts as shown in the following illustration.

The following illustration shows an example of creating an XBar-S chart in iMonitor Designer using the SPC options on the left side of the window.