What AE-ACK-B Is
AE-ACK-B (Alarm and Event-Acknowledgment Execute-B) is the BACnet Interoperability Building Block (BIBB) for a device that executes AcknowledgeAlarm: the originating object, on receiving the request, records that a human operator has seen a specific transition and updates Acked_Transitions to say so.
A device claiming AE-ACK-B is the far end of the round trip that starts when an operator clicks acknowledge at a workstation. AE-ACK-A is the workstation’s BIBB for initiating that request; AE-ACK-B is the controller’s for executing it.
Why the Bookkeeping Matters
Acked_Transitions is a BACnetEventTransitionBits, one bit each for TO-OFFNORMAL, TO-FAULT, and TO-NORMAL. AcknowledgeAlarm carries the specific transition and its timestamp, and the executing device has to match it against the transition it actually recorded before marking the bit. Get that match wrong and one of two failures follows: an alarm an operator already handled keeps re-notifying, or worse, an alarm that re-fires after being acknowledged stays silently marked acked and never surfaces again.
The second failure is the one that costs money: a device whose bookkeeping does not distinguish a new transition from an already-acknowledged one of the same type will not notify again when the condition returns. The full failure mode and the field test for it are worth reading before you assume a device handles this correctly.
| Field on the request | What it has to match |
|---|---|
| Event object identifier | The specific alarming object |
| Event state acknowledged | The transition being acknowledged (TO-OFFNORMAL, TO-FAULT, TO-NORMAL) |
| Time stamp | The specific occurrence, so a new transition of the same type is not silently absorbed |
Where You Meet It in the Field
Any controller an operator can acknowledge an alarm on is claiming AE-ACK-B. It matters most on equipment prone to nuisance re-trips, sticking valves, chattering contacts, anything that clears and re-fires, because that is exactly the pattern the bookkeeping has to get right.
[!WARNING] Test the re-fire case, not just the first alarm. Acknowledge an alarm, force the condition to clear and return, and confirm the device notifies again. A device that passes a single acknowledge-and-clear test can still fail this one.
What Chipkin Provides
The CAS BACnet Stack supports AE-ACK-B today: AcknowledgeAlarm execution and acknowledgeable-alarm bookkeeping across the algorithms it implements. Talk to us about testing your own re-fire scenarios against it.