National Instruments BridgeVIEW - Manual (Page 82)

Chapter 3 Tag Configuration
BridgeVIEW User Manual 3-24 © National Instruments Corporation
What Is Deadband?
In process instrumentation, deadband is the range through which an input
signal can vary without initiating an observable change in output signal.
Deadband usually is expressed in percent of full scale. Although the term
deadband generally applies only to analog tags, other tag types have a
limited type of deadband. A checkbox allows you to determine if updates
to the RTDB and historical data files should occur with any new data from
the device server or if the value has changed.
Note The BridgeVIEW Engine performs historical logging and alarm management
operations based on new values in the RTDB. If you set the Update Deadband too
high, the RTDB might not be updated. This might result in inadequate historical
logging or alarm management.
How Do You Use Deadband to
Increase Engine Throughput?
The BridgeVIEW Engine uses Update Deadband and Log Deadband
values to eliminate unnecessary processing on minor data value changes.
Deadband allows you to define a significant change. The Engine ignores an
operation if the change in data is not considered significant. Deadband is
expressed as percent of full scale. For example, if the tag engineering range
is 0 to 200 liters, a deadband of 5% is 10 liters. In addition, through I/O
group configuration, you can configure a server to apply a deadband to any
items associated with that I/O group. Not all servers implement deadbands.
OPC servers support deadbands.
Set Initial
Value all Determines whether an initial value is used for this tag. If Set
Initial Value is OFF for this tag, the tag value is marked as
uninitialized until its value is updated.
Initial Value all The initial value used for this tag when Set Initial Value is ON.
If the tag is an Output only or Input/Output tag, the BridgeVIEW
Engine sends the Initial Value to the server at Engine startup.
If the tag is an Input only or Memory tag, the Initial Value is
stored in the RTDB at startup.
Table 3-4. Operations Configuration Attributes (Continued)
Attribute
Applies to
Data Types Description