Quality and Process Methods > EWMA Control Charts > The EWMA Control Chart Platform Options
Publication date: 04/12/2021

The EWMA Control Chart Platform Options

The EWMA Control Chart red triangle menu contains the following options:

Show Limits

Shows or hides the upper and lower decision limits in the EWMA chart, X chart, and residuals chart.

Show Center Line

Shows or hides the center line in the EWMA chart, X chart, and residuals chart.

Show Shift Lines

Shows or hides the vertical lines in the EWMA chart that designate shifts. Shift lines are drawn at the start of a shift. A shift start is defined as the first point after the EWMA value crosses the center line in a particular direction.

A positive shift occurs when the EWMA value exceeds the upper limit on the chart. The start of the shift is defined as the first point after the most recent EWMA value below the Target line.

A negative shift occurs when the EWMA value falls below the lower limit on the chart. The start of the shift is defined as the first point after the most recent EWMA value above the Target line.

Test Beyond Limits

Shows or hides a red circle around any point that is above the upper limit or below the lower limit in the EWMA and XBar charts.

Show ARL

Shows or hides the Average Run Length (ARL) report. See Average Run Length (ARL) Report for EWMA Control Charts.

Control Panel

Shows or hides a report of the current values of the parameters. This report enables you to change the parameter values in the EWMA chart.

Parameters Report

Shows or hides a report of the current values of the parameters.

Constant Limits

Specifies that the EWMA chart limits are calculated using an asymptotic expression so that the limits on the EWMA chart are constant.

Caution: The Constant Limits option has no effect when the sample sizes are not equal across subgroups.

Save Summaries

Creates a new data table that contains statistics for each subgroup in the EWMA chart. The following statistics are saved to the new data table: the subgroup number, the subgroup label, the subgroup size, the subgroup mean, an indicator of shift starts, a value that indicates each interval between shift starts, the exponentially weighted moving average of each subgroup, the number of positive and negative consecutive run counts, and the LCL and UCL values. The forecast value is saved in the last row of the summary table.

Reset to Defaults

Resets all parameters back to their default values. If a Lambda value has been specified in the Lambda platform preference, the Lambda value is reset to the value specified in the platform preference.

Note: When the Y variable has a Spec Limits column property that contains a value for Target, the Reset to Defaults option sets the Target to the Target value in the Spec Limits column property.

Restart EWMA After Empty Subgroup

Specifies how calculations for the moving average and limits are handled when there are empty subgroups. A subgroup can be empty if all the observations for the subgroup are missing values or are in excluded rows. If this option is selected, the calculations restart in the first nonmissing subgroup that follows an empty subgroup. The restart of the calculations resets the moving average to the overall mean. If this option is not selected, the EWMA calculations continue with the most recent nonmissing subgroup moving average.

Use Overall Mean for Target

(Available only when the Y variable has a Spec Limits column property that contains a value for Target.) Sets the Target in the EWMA chart to the overall mean of the Y variable. If this option is not selected, the Target in the EWMA chart is set to the Target value in the Spec Limits column property.

Overlay Charts

Specifies whether the individual location values are overlaid on the EWMA chart. When this option is selected, the Location chart is no longer shown. Instead, the points from the Location chart appear on the EWMA chart as unconnected gray Xs. The limits from the Location chart do not appear on the EWMA chart, unless the Show X Limits on Overlay Charts option is selected.

Show X Limits on Overlay Charts

(Available only when the Overlay Charts option is selected.) Shows or hides the limits from the Location chart on the EWMA chart when the Overlay Charts option is selected. When the Location chart limits are shown on the EWMA chart, they appear as dashed lines.

Note: The Tests Beyond Limits option is applied to the Location chart values in the Overlay Chart only when the Show X Limits on Overlay Charts option is selected.

Lambda Slider

Shows or hides a slider control that enables you to change the value of the Lambda parameter interactively.

Show X Chart

Shows or hides the Location chart below the EWMA chart.

Note: When the Overlay Charts option is selected, the Show X Chart option shows or hides the individual location values and limits that are overlaid on the EWMA chart.

Show Residuals Chart

Shows or hides a chart of residuals.

Alarm Script

Enables you to write and run a script that indicates when the data fail special causes tests. Results can be written to the log or spoken aloud, and there is an option to include an explanation of why the test failed. You can also send results to an email using the custom script option.

As an Alarm Script is invoked, the following variables are available, both in the issued script and in subsequent JSL scripts:

qc_col is the name of the column

qc_test is the test that failed

qc_sample is the sample number

Tip: After an alarm script is specified, the alarm script is invoked when the Test Beyond Limits option is turned on.

See Run Alarm Scripts in the Scripting Guide for more information about writing custom Alarm Scripts.

See Redo Menus in Reports and Save Script Menus in Reports in Using JMP for more information about the following options:

Redo

Contains options that enable you to repeat or relaunch the analysis. In platforms that support the feature, the Automatic Recalc option immediately reflects the changes that you make to the data table in the corresponding report window.

Save Script

Contains options that enable you to save a script that reproduces the report to several destinations.

Save By-Group Script

Contains options that enable you to save a script that reproduces the platform report for all levels of a By variable to several destinations. Available only when a By variable is specified in the launch window.

Want more information? Have questions? Get answers in the JMP User Community (community.jmp.com).