Chapter 3
Tag Configuration
©
National Instruments Corporation
3-37
This type of situation clogs event files with redundant information and
can cause operators some frustration in having to acknowledge alarms
constantly when the tag has not changed significantly. You can use the
Alarm Deadband to alleviate this problem.
For the tag to go into alarm, it must go above the exact Alarm Value (in the
above example, 40). However, to be considered normal again, it must leave
the Alarm Value by an amount greater than the Alarm Deadband. For
example, if the range is 0 to 100 degrees Celsius, an Alarm Deadband of
1.0% (one degree Celsius) eliminates unnecessary events. Table 3-9 shows
examples of events with Alarm Deadband set to 1.0%.
How Do You Keep an Alarm Unacknowledged
after the Alarm Returns to Normal?
While editing a tag, select the Alarm Acknowledgement Mode ring and
choose either Auto Ack on Normal or User Must Ack.
Auto Ack on Normal
With this option enabled, when a tag returns to normal state, the alarm
is automatically acknowledged. A message is logged to the event file if
event logging is turned on for the tag. By default, Auto Ack On Normal
is enabled.
9:15:15
40.1
Yes
HI
9:15:20
38.5
Yes
Normal
Table 3-9.
Events with Alarm Deadband = 1.0%
Time
Value
Event
Alarm Type
9:15:05
40.1
Yes
HI
9:15:10
39.9
No
HI
9:15:15
40.1
No
HI
9:15:20
38.5
Yes
Normal
Table 3-8.
Events with Alarm Deadband = 0.0% (Continued)
Time
Value
Event
Alarm Type
