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Chapter 3

Tag Configuration

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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%

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)