National Instruments BridgeVIEW Tag Attributes VIs

Chapter 7 Advanced Application Topics

Tag Attributes VIs

There is a set of VIs in the Tag Attributes palette with which you can read

or change configuration information about tags programmatically. Most

of these tag attributes are parameters you can configure for a tag with the

Tag Configuration Editor. They fall into five categories:

• General Tag Information

• I/O Connection

• Operations

• Scaling

•Alarms

Note Not all parameters configured in the Tag Configuration Editor can be changed

programmatically. However, if you want to make persistent changes for several

dynamic attributes in the Tag Configuration Editor, such changes can be applied

to a running Engine.

You can programmatically take a tag on or off scan. If a tag is off scan,

it is not processed or updated in the Real-Time Database, alarms are not

calculated, and data is not logged. You can start these activities by putting

that tag back on scan.

There are specific VIs you can use to obtain certain tag information,

such as the Get Tag Logging Info VI or the Get Tag Alarm Enabled VI.

For the Set Tag Attribute or Set Multiple Tag Attributes VIs, an error is

returned if the Engine is not running. In addition, tag attribute changes

only affect the current Engine process until they are subsequently

changed or the Engine stops.

If the Engine is running, you can change tag attributes programmatically

with the Set Tag Attribute VI, Set Multiple Tag Attributes VI, or the Tag

Configuration Editor. These VIs return an error if the Engine is not running.

Tag attribute changes stay in effect in the current run only. If you stop the

Engine and start it again, the changes are lost. Use these VIs in your

application when you want to change attributes of a tag dynamically, as

with logging, alarm, or scaling information, or taking a tag on or off scan.

For a complete description of the Tag Attributes VIs, refer to AppendixA,

HMI Function Reference.