Using BACnet Notification Class Objects

In a BACnet network, a device is able to generate an unsolicited message when a pre-configured condition is met. The mechanism is often referred to as Alarm/Event Notification.

Alarm and event notifications are generated by the Notification Class object within a physical BACnet device. The Notification Class object's properties define how notifications are controlled.

• The conditions under which the messages are sent.
• The list of recipients, on the BACnet network, to which the message is sent.

 PcVue can receive such messages and map the change of state information therein to an alarm or bit variable.

A Notification Class object's behavior also includes the ability for the sender to expect an acknowledgement of the notification from recipients. How the acknowledgement is managed depends on the setting Acknowledge alarm/event notifications. See the topic BACnet settings.

A physical BACnet device can have any number of Notification Class instances. Messages from the Notification Class object are triggered by other, so-called source, objects in the device and are typically a consequence of a change to the Present Value. For example, an Analog Input can trigger a notification if the Present Value exceeds the High Limit. The notification message always includes information about the change of state of the event, and the Present Value of the triggering object. It may also contain other properties depending on the object type. For example, a notification generated by an Analog Input object also contains the Deadband, High Limit and Low Limit.

A Notification Class object's recipient list declares which devices are to receive the notification message and hence, if it is to receive such messages, PcVue must be registered in the list. The BACnet driver is able to register itself with an existing Notification Class object, or to create, and register with, an entirely new Notification Class object.