When a selected multistate control point is in a specified shutdown state, the Auto Shutdown object suppresses alarm reporting from a list of dependent objects to prevent nuisance alarms. The Auto Shutdown object accomplishes this by sending an enable/disable command to each of the dependent object's Alarm objects, based on the control point’s current state (the value of the Control attribute) and the defined shutdown state. For BACnet intrinsic alarming and Event Enrollment objects, these commands set and reset the BACnet Alarm Event Enable property flags (To Off Normal, To Fault, and To Normal) that cause or prevent alarms. A startup delay is provided so that points are not released immediately from shutdown.
An example of a use for the Auto Shutdown object is to prevent alarms set to monitor the discharge air temperature of a fan when that fan is turned off. When the fan is turned off, the fan state value is sent to the Auto Shutdown object. The Auto Shutdown object then evaluates the current state of the point against the Shutdown State defined in the Auto Shutdown object. If the current point state matches the Shutdown State, the Auto Shutdown object sends a Disable command to the Alarm object of every referenced dependent object in the Dependents list.
Consequently, when the fan is turned back on, the Auto Shutdown object again evaluates the current state and, if the current state does not match the Shutdown State, starts the Startup Delay timer. Once the timer expires, the Auto Shutdown object sends an Enable command to the Alarm object of every referenced dependent object in the Dependents list.