BACnet Event Log Object

What the Event Log Object Is

The Event Log object, defined in Clause 12.27 of ANSI/ASHRAE 135-2024, is how a BACnet device keeps a history of event notifications rather than of property values. Each record holds a received or generated event notification, timestamped, in an internal buffer for later retrieval. Where a Trend Log answers “what was this value over time,” an Event Log answers “what alarms and events happened.”

Which notifications land in the buffer is a local matter, and it can include events that were never transmitted as an APDU (Application Protocol Data Unit). The buffer is read back with the ReadRange service, and writing zero to Record_Count clears it. When an Event Log supports intrinsic reporting it applies the BUFFER_READY event algorithm, notifying recipients once Notification_Threshold new records have accumulated.

Where You’ll See It

• Alarm history. An Event Log gives operators an on-device record of alarm and event activity that survives independent of the head end (the central BMS server).
• Audit and forensics. Because it can capture events never sent on the wire, an Event Log helps reconstruct what a controller experienced during an incident.
• Automatic collection. With intrinsic reporting enabled, BUFFER_READY signals a fileserver to fetch the new records with a ReadRange request.

Required Properties

Clause 12.27 requires every Event Log object to provide these properties. Datatypes are the spec’s names: BOOLEAN is a true/false flag, Unsigned an integer, BACnetLIST of BACnetEventLogRecord is the timestamped buffer of notifications, and the other BACnet-prefixed types are structured values defined by the standard.

Property	Datatype	What it holds
Object_Identifier	BACnetObjectIdentifier	The object’s type and instance number, unique within the device
Object_Name	CharacterString	The human-readable point name, unique within the device
Object_Type	BACnetObjectType	Always event-log for this object
Enable	BOOLEAN	Writable; turns logging on and off
Stop_When_Full	BOOLEAN	When true, logging stops once the buffer fills instead of overwriting
Buffer_Size	Unsigned	The maximum number of records the buffer holds
Log_Buffer	BACnetLIST of BACnetEventLogRecord	The stored timestamped event notifications, read with ReadRange
Record_Count	Unsigned	Writable; the number of records in the buffer, and writing zero clears it
Total_Record_Count	Unsigned32	The running total of records ever collected. Monotonic: it does not decrease on wrap, and rolls over from 4294967295 to 1, used as the sequence number
Status_Flags	BACnetStatusFlags	Four health flags: in-alarm, fault, overridden, out-of-service
Event_State	BACnetEventState	The object’s current event state. It stays normal for buffer-ready reporting, which is dispatched as a TO-NORMAL transition from NORMAL. See BUFFER_READY
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	The list of properties this instance actually implements

Optional Properties

The properties integrators meet most are Start_Time and Stop_Time (the window during which the log collects) and the intrinsic-reporting group that drives automatic fetching. The intrinsic-reporting group appears or is absent as a set.

Property	Datatype	Group
Description	CharacterString	General
Start_Time	BACnetDateTime	Logging
Stop_Time	BACnetDateTime	Logging
Reliability	BACnetReliability	Fault detection
Notification_Threshold	Unsigned	Intrinsic reporting
Records_Since_Notification	Unsigned	Intrinsic reporting
Last_Notify_Record	Unsigned	Intrinsic reporting
Notification_Class	Unsigned	Intrinsic reporting
Event_Enable	BACnetEventTransitionBits	Intrinsic reporting
Acked_Transitions	BACnetEventTransitionBits	Intrinsic reporting
Notify_Type	BACnetNotifyType	Intrinsic reporting
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	Intrinsic reporting
Event_Message_Texts	BACnetARRAY[3] of CharacterString	Intrinsic reporting
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	Intrinsic reporting
Event_Detection_Enable	BOOLEAN	Intrinsic reporting
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	Intrinsic reporting
Event_Algorithm_Inhibit	BOOLEAN	Intrinsic reporting
Reliability_Evaluation_Inhibit	BOOLEAN	Fault detection
Audit_Level	BACnetAuditLevel	Auditing
Auditable_Operations	BACnetAuditOperationFlags	Auditing
Tags	BACnetARRAY[N] of BACnetNameValue	Tagging and profile
Profile_Location	CharacterString	Tagging and profile
Profile_Name	CharacterString	Tagging and profile

Related Objects

• Trend Log: logs a property’s value over time rather than event notifications.
• Trend Log Multiple: logs a set of properties in lockstep.
• Notification Class: routes the BUFFER_READY notification to its recipients.

What Chipkin Provides

The Event Log object stores event notifications in a ReadRange-accessible buffer with BUFFER_READY intrinsic reporting. Talk to us about modeling your device’s points.

Related Pages

• BACnet
• BACnet Objects
• BACnet ReadRange Service
• BACnet Trend Log Object
• BACnet Object Types & Properties Reference
• BACnet Total_Record_Count vs Record_Count: what the counters mean and what actually loses history
• BACnet BUFFER_READY: The Event That Fires Without a State Change: why the notification this object depends on silently never arrives