Large Analog Value

A Large Analog Value object holds a double-precision floating point number. Use it when a normal analog object’s single-precision value is not accurate enough, such as for cumulative energy or large totals.

Typical uses

• Report lifetime energy consumption without rounding errors
• Expose a very large flow total
• Hold a precise calculated value from an analytics engine
• Accept a high-precision setting from a client

Key properties

Property	What it holds
Present_Value	The current value as a double-precision number.
Units	The engineering units of the value.
COV_Increment	The change in value that triggers a change-of-value notice.
Min_Pres_Value	The lowest value the object accepts. Optional.
Max_Pres_Value	The highest value the object accepts. Optional.
Resolution	The smallest change the value can show. Optional.

How it behaves

A Large Analog Value is a plain value unless it has a priority array and a relinquish default, in which case clients command it with prioritised writes. Where it reports events itself, the standard pairs it with the DOUBLE_OUT_OF_RANGE algorithm: an alarm when the value leaves its low and high limits, with a deadband on the way back. It sends change-of-value notices when the value moves by COV_Increment.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_LARGE_ANALOG_VALUE build option and add each object with BACnetStack_AddObject. Serve Present_Value with the callback you register with BACnetStack_RegisterCallbackGetPropertyDouble, and accept writes with the BACnetStack_RegisterCallbackSetPropertyDouble callback. It becomes commandable when you enable both PriorityArray and RelinquishDefault with BACnetStack_SetPropertyEnabled; the stack then reads the priority array through your callbacks instead of calling the plain Present_Value callback. Arm limit alarms with BACnetStack_SetAlarmsAndEventsForObjectEnabled and then BACnetStack_SetIntrinsicDoubleOutOfRangeAlgorithm. The stack has no fault out-of-range setter for this type: BACnetStack_SetFaultOutOfRangeAlgorithmReal refuses it.

Related object types

Analog Value, Integer Value, Positive Integer Value, Accumulator

Properties

The properties ASHRAE 135-2024 clause 12.39 defines for this object type.

How to read the table:

• Conformance is what the standard asks of every object of this type: R is required, W is required and writable by a client, O is optional. A digit after the letter marks a condition in the standard that decides when the property is present or writable, such as support for intrinsic reporting.
• Present by default: yes means the stack presents the property as soon as you add the object; no means it is optional and you turn it on with BACnetStack_SetPropertyEnabled. This is the stack’s starting setup, so it can differ from the conformance code.
• Writable is whether a client can write the property by default. Change it with BACnetStack_SetPropertyWritable.
• not in profile means the stack does not offer this property for this object type.
• Value when your callback does not answer: “Held by the stack” means the stack stores and serves the value itself and does not ask your callbacks. Otherwise it is the value the stack answers when your callback declines or is not registered.

Property	Datatype	Conformance	Present by default	Writable	Value when your callback does not answer
Object_Identifier	BACnetObjectIdentifier	R	yes	no	Held by the stack.
Object_Name	CharacterString	R	yes	no	"Object <type>,<instance>", such as "Object 0,1" for Analog Input 1.
Object_Type	BACnetObjectType	R	yes	no	Held by the stack.
Description	CharacterString	O	no	no	""
Present_Value	Double	R1	yes	no (yes while Out_Of_Service is true)	No default: value-not-initialized. Once Priority_Array and Relinquish_Default are enabled, built by the stack from the priority array your callbacks serve.
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	O4	no	no	0
Reliability	BACnetReliability	O	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	O	no	no	false
Units	BACnetEngineeringUnits	R	yes	no	95 (no units)
Priority_Array	BACnetARRAY[16] of BACnetOptionalDouble	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	Double	O2	no	no	No default: value-not-initialized until a callback or a client write supplies one.
COV_Increment	Double	O3	no	no	0.0
Time_Delay	Unsigned	O4,6	no	no	0
Notification_Class	Unsigned	O4,6	no	no	0
High_Limit	Double	O4,6	no	no	0.0
Low_Limit	Double	O4,6	no	no	0.0
Deadband	Double	O4,6	no	no	0.0
Limit_Enable	BACnetLimitEnable	O4,6	no	no	An empty bit string.
Event_Enable	BACnetEventTransitionBits	O4,6	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O4,6	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O4,6	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O4,6	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O6	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O6	no	no	""
Event_Detection_Enable	Boolean	O4,6	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O6	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O6,7	no	no	false
Time_Delay_Normal	Unsigned	O6	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O8	no	no	false
Min_Pres_Value	Double	O	no	no	0.0
Max_Pres_Value	Double	O	no	no	0.0
Resolution	Double	O	no	no	0.0
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Fault_High_Limit	Double	O9	no	no	0.0
Fault_Low_Limit	Double	O9	no	no	0.0
Current_Command_Priority	BACnetOptionalUnsigned	O2	no	no	Built by the stack from your callbacks.
Value_Source	BACnetValueSource	O10,12,14	no	no	No default: the read fails.
Value_Source_Array	BACnetARRAY[16] of BACnetValueSource	O11,13	no	no	No default: the read fails.
Last_Command_Time	BACnetTimeStamp	O11,13	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O13	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O15	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O15	not in profile	not in profile	No default: the read fails.
Audit_Priority_Filter	BACnetOptionalPriorityFilter	O15	not in profile	not in profile	No default: the read fails.
Tags	BACnetARRAY[N] of BACnetNameValue	O	no	no	No default: the read fails.
Profile_Location	CharacterString	O	no	no	""
Profile_Name	CharacterString	O	no	no	""