A tag in Wonderware Historian is the equivalent of a point or accumulator in ClearSCADA.
When you configure a ClearSCADA point or accumulator for historical data storage, ClearSCADA automatically uses HCAL to create a new tag in Wonderware Historian. It does this when it first exports data for the point or accumulator. ClearSCADA will give the tag a name with the following format:
[<prefix>.]<object name>.<aggregate name>
For example, CS.Internal Analog Point.Historic
A tag name can be a maximum of 256 characters in length. Ensure that the prefix and object names are not too long. For more about the Tag Name Prefix, see Configure a Wonderware Historian Database Item.
Tags also have a description associated with them. By default, ClearSCADA sets the description to the class name and object ID of the point or accumulator. This is so that you can match tags in Wonderware Historian with items in the ClearSCADA database. For example, after renaming an item in ClearSCADA (see Troubleshooting Wonderware Historian Driver Operation). If you don't want to use the default description, you can change it by creating a custom ClearSCADA metadata field to configure the TagDescription property (see Configure Wonderware Historian Tag Properties from ClearSCADA) and (see TagDescription).
If you do one of the following in ClearSCADA:
- Delete a point or accumulator
- Disable historic storage on a point or accumulator
ClearSCADA will use HCAL to delete the tag from each Wonderware Historian server.
If you modify a point or accumulator to remove a historic export, ClearSCADA will use HCAL to delete the tag from the Wonderware Historian server for each removed export.
If you change the tag prefix in ClearSCADA, then ClearSCADA will only apply the new prefix to points or accumulators:
- To which ClearSCADA has not yet exported any data
- That you subsequently create.
All existing points or accumulators will continue to use their existing tag names. This also applies to database items that you rename or move in ClearSCADA.
You can use the Status display to view the tag names associated with each point or accumulator (see Wonderware Historian Driver-Specific Status Display Attributes).