5.7.3. Additional Information for Deadband

Deadband is needed for a value that flickers or fluctuates a lot. If a tag value keeps fluctuating around the alarm limit, then similar alarm may keep coming on and going off and thus generates unnecessary repeated alarms. This problem can be avoided with deadband, so alarm shall go off only when the value go below the limit plus deadband either in actual value or in percentage.

For instance, if high limit is set to 80, and deadband set to 10, then alarm shall occur when the value is greater than 80. However, alarm will not go off when the value fall across 80, but alarm shall go off only when the value fall below 70. Obviously alarm shall reoccur as usual if it rise above 80 again.

Deadband also can be entered as time delay in seconds, whereby alarm will be considered as once if it oscillates multiple times across the limit within the specific time frame. On the other hand, alarm will *not* be triggered if it doesn't stay longer than the specified duration. For instance, a spike that runs less than entered duration will be ignored.