BACnet: Event Enrollment Object

The Event Enrollment object is defined by the standard as information related to the management of events for BACnet systems. Events are essentially changes in the value of any property concerning any object that meets specific criteria.

The central purpose for the Event Enrollment object is to define an event, and offer the developer a connection between the event occurrence and the transmission of notification messages.

The Event Enrollment object contains the following information for effective operation:

• Event Type Description
• Event Occurrence Notification
• Device Notification

The following table will present the actual properties and associated datatypes of the Event Enrollment object from the BACnet standard:

Property	Datatype
Object_Identifier	BACnet Object Identifier
Object_Name	Character String
Object_Type	BACnet Object Type
Description	Character String
Event_Type	BACnet Event Type
Notify_Type	BACnet Notify Type
Event_Parameters	BACnet Event Parameter
Object_Property_Reference	BACnet Device Object Property Reference
Event_State	BACnet Event State
Event_Enable	BACnet Event Transition Bits
Acked_Transitions	BACnet Event Transition Bits
Notification_Class	Unsigned
Event_Time_Stamps	BACnet Array (3) of BACnet Time Stamp
Profile_Name	Character String

The BACnet standard states that there's a specific relationship among three properties:

• Event_Type
• Event_State
• Event_Parameters

The Event_Type represents the algorithm used to determine the Event_State. The Event_Parameters property provides certain parameters required by the algorithm. The developer should pay special attention to the relationship of these three properties.

The following table from the standard will examine the three properties and their associated values:

Event_Type	Event_State	Event_Parameters
Change_of_ Bitstring	Normal OffNormal	Time_Delay Bitmask List_of_Bitstring_Values
Change_of_State	Normal OffNormal	Time_Delay List_of_Values
Change_of_Value	Normal OffNormal	Time_Delay Bitmask Referenced_Property_Increment
Command_Failure	Normal OffNormal	Time_Delay Feedback_Property_Reference
Floating_Limit	Normal High_Limit Low_Limit	Time_Delay Setpoint_Reference Low_Diff_Limit High_Diff_Limit Deadband
Out_of_Range	Normal High_Limit Low_Limit	Time_Delay Low_ Limit High_ Limit Deadband
Buffer_Ready	Normal	Notification_Theshold
Change_of_Life_Safety	Normal OffNormal Life_Safety_Alarm	Time_Delay List_of_Alarm_Values List_of_Life_Safety_Alarm_Values Mode_Property_Reference

The next two examples from the standard will reveal the Event Enrollment object structure from an actual automation application. Specifically, the two examples will involve temperature control in a certain room of a building:

Property: Object_Identifier = (Analog Input, Instance 2)
Property: Object_Name = "Zone1_Temp"
Property: Object_Type = ANALOG_INPUT
Property: Present_Value = 86.0
Property: Description = "Receptionist Lobby Temp"
Property: Device_Type = "PT 3K RTD"
Property: Status_Flags = {FALSE, FALSE, FALSE, FALSE}
Property: Event_State = NORMAL
Property: Reliability = NO_FAULT_DETECTED
Property: Out_Of_Service = FALSE
Property: Update_Interval = 5
Property: Units = DEGREES_FAHRENHEIT
Property: Min_Pres_Value = 55.0
Property: Max_Pres_Value = 95.0
Property: Resolution = 0.1

The Analog_Input object above is assumed for the following Change_of_Value Event example, and the object is located in Device 12.

Property: Object_Identifier = (Event Enrollment, Instance 2)
Property: Object_Name = "Zone1TempCOV"
Property: Object_Type = EVENT_ENROLLMENT
Property: Description = "Zone 1 Temperature COV"
Property: Event_Type = CHANGE_OF_VALUE
Property: Notify_Type = EVENT
Property: Event_Parameters = (5, 0.25)
Property: Object_Property_Reference = ((Device, Instance 12),(Analog Input, Instance 2), Present_Value)
Property: Event_State = NORMAL
Property: Event_Enable = (TRUE, FALSE, FALSE)
Property: Acked_Transitions = (TRUE, TRUE, TRUE)
Property: Event_Time_Stamps = ((23-MAR-95,18:50:21.2),(*-*-*,*:*:*.*),(23-MAR-95,19:01:34.0))

Written by: Scott Cosby