A Master Tag is a logical collection of tags from multiple process areas within a single location. For example, tags whose data come from the same type of equipment or tags that share common limits might be grouped together. Tags linked to a master tag are called child tags.
A Master Tag is not an actual tag itself, but a placeholder that behaves like one of its child tags depending on a process-specific context. A Master Tag-compatible display uses a process selector to define this context. Because a Master Tag can behave like its many child tags, a single display that utilizes this functionality can accomplish the work of many displays. Additionally, indexed master tags can be used to represent logical groupings of child tags that are replicated in multiple process areas.
Limits can be defined for a master tag; a child tag can then be configured either to inherit these limits or to use its own limits. This feature can greatly reduce the effort of maintaining limits while more naturally reflecting the logic behind common limit specifications.
How and when the master-child relationship functions is configured primarily in the Master Tag Editor and in displays.