Variable Settings
Variable settings such as the statistical settings, specification limits, images, and tags may be set from the Variable Settings dialog.
To edit variable settings left-click the Project Setup icon
located on the main window toolbar. This icon launches the Project Setup dialog.
The Project Setup dialog contains two windows. The left-hand-side (LHS)
window contains all parts and devices within the project. The right-hand-side (RHS)
window contains all variables for a selected part.
To edit variable settings, select a part from the part list (left-hand side of the Setup dialog), then double-left
click a variable from the variable list (right-hand-side of the Setup dialog). The Variable Settings window will appear.
The start subgroup may be specified by selecting the
Statistical Settings tab.
The start subgroup is the subgroup after which process control is evaluated. For example, if a process
has collected ten subgroups and the start subgroup is subgroup number 2, then statistical control will
be evaluated using only subgroups 2 through 10. It is often necessary to change the start subgroup after statistical
control has been evaluated and a special causes of variation identified. In such a case, the process may likely be
changed to eliminate the special cause of variation. Once changed, new data should be treated separately from
data prior to the change. The start subgroup may be set to remove those old subgroups from the statistical analysis.
Two subgroups are required to determine control limits. If the start subgroup is set such that the
number of subgroups is less than two then several options are available to handle control limits: 1) Exisiting
control limits should be used, or 2) Statistical control should not be evaluated until 2+ subgroups
have been collected.
If statistical control should continue to be evaluated from existing control limits
then select Use existing limits until 2+ subgroups have been collected. If statistical control
should not be evaluated until new control limits are calculated then select Ignore limits until 2+ subgroups
are collected.
Image windows are used to display schematics,
drawings, blueprints, or any image alongside control charts and spreadsheets.
Users may then visually confirm they are measuring the correct part feature, and prevent
themselves from mistakenly entering the wrong data.
Images appear in the Image window. To define a variable image, select the Browse button from
the Variable Settings dialog and select any JPG, BMP, or PNG image (JPG, BMP, and PNG are the only available image formats).
Image windows may display a part image or a variable image. A part image may be specified from the
Part Settings dialog, and a variable image may be specified from the variable settings dialog.
The Image Window will default to
the part image if specified. To default to the variable image, select the Use Variable Image check box from the variable settings dialog.
Specification limits may be enetered from the Specification Limits page. Three limits are available: 1) Upper specification limit,
2) lower specification limit, and 3) the target or central specification limit. To set the target specification limit to the average
of the upper and lower specification limit, select the Use Avg check box.
Specification limits are displayed on control charts and
capability charts. Out-of-spec samples are defined by the specification limits. For example if the upper specification limit is 5.23, and
a collected sample has a value of 6.34, then the sample will be determined an out-of-spec sample and will be identified on the control charts. If
an out-of-spec sample is identified, SPC Works may set an alarm (if an alarm is active). See Action Devices for
more information regarding Alarms.
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