This OPC UA ObjectType represents an object that monitors a single property of a referenced object and logs its value and timestamp into an internal buffer when a set of pre-defined conditions are met.

Figure 31 shows an overview for the BACnetTrendLogType with its Properties and related ObjectTypes. It is formally defined in Table 39.

Figure 31 – BACnetTrendLogType overview

The BACnetTrendLogType ObjectType is formally defined in Table 39.

Table 39 – BACnetTrendLogType Definition

Attribute		Value
BrowseName		BACnetTrendLogType
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of the BACnetTrendLogBaseType defined in 7.20.3.10.
0:HasProperty	Variable		COV_Resubscription_Interval	0:UInteger	0:PropertyType	O
0:HasProperty	Variable		Client_COV_Increment	BACnetClientCOV	0:PropertyType	O
0:HasProperty	Variable		Log_DeviceObjectProperty	BACnetDeviceObject PropertyReference	0:PropertyType	O
0:HasComponent	Variable		Log_Buffer	BaseDataType	0:BaseData VariableType	M

The BACnetTrendLogType ObjectType is a concrete type and can be used directly.

This OPC UA Property, of DataType UInteger, represents the BACnet property COV_Resubscription_Interval.

The COV_Resubscription_Interval specifies the time in seconds between COV resubscriptions. The first COV subscription is issued when the trend log begins operations or when the Enable variable value becomes true.

This OPC UA Property, of DataType BACnetClientCOV, represents the BACnet property Client_COV_Increment. The BACnetClientCOV DataType is defined in 10.6.3.

The Client_COV_Increment value indicates the increment that is used to determine whether a change of value has occurred.

This OPC UA Property, of DataType BACnetDeviceObjectPropertyReference [], represents the BACnet property Log_DeviceObjectProperty. The BACnetDeviceObjectPropertyReference DataType is defined in 10.5.9.

The Log_DeviceObjectProperty variable specifies the Device Identifier, Object Identifier, and Property Identifier of the property to be trend logged.

This OPC UA Variable represents the BACnet property Log_Buffer. It represents a list of logged values and can only be accessed with with the BACnet service ReadRange. Therefore, the OPC UA representation requires the AccessLevel HistoryReadable to allow access of the logged values through OPC UA Service HistoryRead (see Table 40).

The current value is not readable since it is not provided through BACnet directly. The BACnetUaMapper may provide the current value by reading the referenced BACnet property that is logged by the BACnet Trend Log object. In this case the AccessLevel can also have the Readable flag set.

Table 40 – Log_Buffer Attribute definition

OPC UA Attribute	Value
BrowseName	Log_Buffer
AccessLevel	HistoryReadable
Historizing	True if BACnet property Enable is True and the current time is between the BACnet property values Start_Time and Stop_Time