Rockwell Automation FactoryTalk View Site Edition Users Guide - Manual (Page 186)

F ACTORY T ALK V IEW S ITE E DITION U SER ’ S G UIDE
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Using direct referencing to eliminate duplication
For some uses in an application, using direct references to tags in devices, or to tags
located in an OPC server’s database, offers advantages over using HMI tags.
For example, use data server tags to add, modify, or delete tags in a device without having
to duplicate the changes in the HMI server’s tag database.
Providing access to complex data types
Some devices (Logix5000 controllers, for example) support data types such as arrays and
structures, which can contain hundreds of member elements.
Use data server tags to reference the tag values directly, and eliminate the need to create
an HMI tag for each member element.
Using the extended capabilities of HMI tags
To take advantage of extended capabilities, such as run-time security, scaling or offsetting
of tag values, or more flexible addressing, you can create HMI tags in FactoryTalk
View Studio, in the Tags editor.
Securing tag or device values
HMI tags let you secure tag or device values at run time.
For example, to prevent users from changing a value in a device, create an HMI tag for
the device’s address, and then assign a security code to the HMI tag. For details, see
“Assigning security codes to HMI tags” on page 5-19.
Scaling and offsetting values
HMI tags provide scale and offset capabilities, which are not supported by some data
servers.
Use scale and offset to modify the raw data that comes from the network device before it
is saved in the computer’s memory, or to modify a value specified in FactoryTalk View
before it is written to a device or data server.
Scale is a multiplication factor—the value from the device is multiplied by the scale.
Offset is a fixed value—after the value from the device is multiplied by the scale, the
offset amount is added.
Specifying minimum and maximum values
With HMI tags, you can specify the minimum and maximum values that can be written
to the network device or data server.
The minimum and maximum values do not affect what is read from the device or server.