Chapter 3
Tag Configuration
3-20
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National Instruments Corporation
Example 2When to Use a Memory Tag
A simple device server returns several items of data that, through a linear
combination of values, represent a meaningful measurement in engineering
units. The design of the device and its server software makes it difficult to
combine these values within the server to make a single tag. The value of
interest is not the individual points but the linear combination of these
I/O points. The operators need historical trends and alarm management
based on this single value.
In this situation, you can define a separate tag for each server item and a
memory tag with engineering range and units of the final measurement.
In the block diagram of the HMI VI, read individual tag values and
calculate the linear combination of values in the diagram. Write the
calculated value to the memory tag in the Real-Time Database and the
BridgeVIEW Engine performs historical logging and alarm calculations
according to the memory tag configuration.
Note
To learn more about how to build HMI VIs, refer to Chapter 4,
.
How Do You Automatically Generate
Tags from Server Information?
Use the Configuration Wizard to create tags from the server information.
The Configuration Wizard is useful if you want the BridgeVIEW Engine
to monitor a large number of the I/O points in your system. To invoke
the Configuration Wizard, press the Configuration Wizard button on the
main screen of the Tag Configuration Editor or select Edit»Configuration
Wizard…. For more information on servers, see Chapter 8,
.
When you run the server configuration utilities for the servers on your
system, you can define devices and items for the I/O points the servers
monitor and control. You can automatically create tags from these items
with the Configuration Wizard. When the tags are created, the tag name,
data type, I/O group, I/O connection, and scaling parameters are
determined by the server information for each server item. The remaining
tag parameters are determined by the default tag parameter settings. You
can edit the default parameters by selecting opening the Tag Configuration
Editor and selecting Configure»Default Parameters….
For IAK and VI-based servers, server information is read from the
Common Configuration Database (CCDB). For OPC servers that support
it, server information is read by browsing the server address space. When
you generate tags, you can either add them to the existing configuration by
