National Instruments BridgeVIEW 用户手册
Chapter 3
Tag Configuration
© National Instruments Corporation
3-19
The Edit… button invokes a server-dependent configuration dialog box,
which you can use to edit the configuration of the selected item. If the
server does not support item configuration, or if the selected item is not
valid, this button is disabled.
which you can use to edit the configuration of the selected item. If the
server does not support item configuration, or if the selected item is not
valid, this button is disabled.
The Delete button invokes a confirmation dialog box. If confirmed,
the selected item is removed from the server configuration.
the selected item is removed from the server configuration.
The Browse… button, which only applies to OPC Servers that support
browsing, invokes the Browse OPC Server dialog box. Use this button
to browse the list of available items and select an item and associated
access path.
browsing, invokes the Browse OPC Server dialog box. Use this button
to browse the list of available items and select an item and associated
access path.
What Is a Memory Tag?
are tags not connected directly to I/O points. They exist only
in the BridgeVIEW RTDB. To configure a memory tag, set the Access
Rights of a tag to Memory.
Rights of a tag to Memory.
When Should You Use a Memory Tag?
Use memory tags when you want to perform alarm calculations,
or log historical data and event information on data that is either a
software-generated value or a combination of values from different
I/O tag readings. Below are some examples illustrating when to use
memory tags.
or log historical data and event information on data that is either a
software-generated value or a combination of values from different
I/O tag readings. Below are some examples illustrating when to use
memory tags.
Example 1When Not to Use a Memory Tag
You do not need to use a memory tag for program variables unless you
want to use the historical and event logging or alarm management
capabilities of the BridgeVIEW Engine.
You do not need to use a memory tag for program variables unless you
want to use the historical and event logging or alarm management
capabilities of the BridgeVIEW Engine.
An HMI displays the trend of a temperature tag and the difference between
the current reading and a previous reading to allow operators to see the
current rate of change in the temperature value. Although the individual
values are logged for historical trends, the current difference is not.
the current reading and a previous reading to allow operators to see the
current rate of change in the temperature value. Although the individual
values are logged for historical trends, the current difference is not.
You can configure the BridgeVIEW Engine to include the tag that reads
temperature. The block diagram of the HMI reads the tag value and passes
it to a real-time trend indicator. The difference between the current reading
and the previous value is calculated in the diagram and passed to a front
panel numeric indicator. The diagram retains the current temperature value
and uses it after taking the next reading. Because the system does not need
to perform any alarm management or historical logging based on the
difference, no memory tag is used.
temperature. The block diagram of the HMI reads the tag value and passes
it to a real-time trend indicator. The difference between the current reading
and the previous value is calculated in the diagram and passed to a front
panel numeric indicator. The diagram retains the current temperature value
and uses it after taking the next reading. Because the system does not need
to perform any alarm management or historical logging based on the
difference, no memory tag is used.