Bridge User Manual

Chapter 3 Tag Configuration

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.

The Delete button invokes a confirmation dialog box. If confirmed,

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.

What Is a Memory Tag?

Memory tags 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.

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.

Example 1When 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.

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.

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.