These options allow you to set the appropriate Control System tag name uniqueness level. Control System tag name uniqueness can be set on the plant level or can be customized. You can also choose to define your Control System tag names as not unique.
To access these preferences, in the Preferences dialog box, in the tree view pane, click 
beside Wiring and then click CS Tags.
CS tag name uniqueness — Use these options to determine at what level in the Wiring module the software prevents duplication of a Control System tag name.
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Custom — Allows access to the following options where you can set the Control System tag name uniqueness level separately for each Control System, or for tag names not assigned to I/O cards.
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Per plant — Allows the use of a specific CS tag name in the plant only once.
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Not unique — Allows the use of the same CS tag name more than once at any level in the plant.
DCS uniqueness
The following options allow you to set the required uniqueness level for a Distributed Control System (DCS):
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Plant — Set uniqueness at the plant level.
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Per panel — Set uniqueness at the panel level.
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Per terminal strip — Set uniqueness at the terminal strip level.
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Not unique — Allow use of the same Control System tag name at any level.
PLC uniqueness
The following options allow you to set the required uniqueness level for a Programmable Logic Controller (PLC):
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Plant — Set uniqueness at the plant level.
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Per panel — Set uniqueness at the panel level.
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Per terminal strip — Set uniqueness at the terminal strip level.
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Not unique — Allow use of the same Control System tag name at any level.
Unassigned CS tag
The following options allow you to set the required uniqueness level for Control System tag names of tags that are not assigned to I/O cards:
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Unique — Allow the use of a CS tag name of an unassigned tag only once.
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Not unique — Allow the use of the same CS tag name for any tag that is not assigned to an I/O card.