Rockwell Automation 9307 FactoryTalk EnergyMetrix - Manual (Page 90)

FactoryTalk EnergyMetrix Software
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5. Once the meter tag has been saved, you can manually refresh tags from the remote
server by entering a start date in the field provided, and clicking the Get roll-up tag
values button.
Set up a Derived Tag
A derived tag is used to log values that are calculated from other meter tags. A derived tag
script defines the tags and mathematical operations that return the desired value. Follow
these steps to create a derived tag.
1. In the Add a Meter Tag window, select Derived as the Meter tag type.
2. Enter a Derived tag script in the entry field.
Note the following:
 The output variable of the script must be Result.
 Meter tags may be specified by using fully qualified tag names or by using the
shortcut method.
 Scripts may include any Derived Tag functions or functions in the .NET system.math
namespace.
 Derived tags should not reference other derived tags, with two exceptions:
 Derived tag functions may reference any tag (including itself) logged previous to
the current time.
 Derived tags are calculated in meter tag ID order, so derived tag functions may
reference other derived tags with lower-numbered meter tag IDs.
If custom value types have been added to a local FactoryTalk
EnergyMetrix server, identical value types must exist in the roll-
up server to prevent roll-up data with an incorrect value type.
Identical value types have the same Value Type ID, description,
units, demand, and consumption flag settings.
If a derived tag script does not set the Result variable then no
value will be inserted into the database.