Rockwell-automation FactoryTalk View Site Edition Users Guide Manual do Utilizador descarregar pdf (Página 186)

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FACTORYTALK VIEW SITE EDITION USER’S GUIDE

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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.

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