Deadband in AlarmWorX64 Server

In the AlarmWorX64 Server, several alarm types have a Deadband field. The deadband of an alarm defines a region where the alarm value can pass under the limit but still not exit the alarm state. It is designed to reduce alarm chattering (where an alarm value hovers around the limit and enters and exits the alarm state repeatedly over a short period of time).

The deadband applies when the alarm leaves the current alarm state (returns to normal or enters a lower state, such as from HiHi to Hi). It does not apply when an alarm enters a new state.

In the case of a Hi or HiHi limit, the alarm value must drop below the limit minus the deadband value before it is considered out of that state. For Lo or LoLo limits, the alarm value must rise above the limit plus the deadband value.

For example, a limit alarm with a Hi limit of 100 and a deadband of 2 will go into the alarm state as soon as it passes 100, but it must drop below 98 to return to normal.