Analog Value

An Analog Value object holds a real number that lives in the device’s memory rather than at a physical terminal. Devices use it for setpoints, calculated values and parameters. Whether a client can change it depends on how you set it up.

Typical uses

• A room temperature setpoint
• A calculated average of several sensors
• A tuning gain for a control loop
• A gateway point mapped from another protocol

Key properties

Property	What it holds
Present_Value	The stored value, a real number.
Units	The engineering unit of the value.
COV_Increment	The smallest change that triggers a change-of-value notification.
Priority_Array	Present only when the object is commandable. It arbitrates between writers.
Relinquish_Default	The value used when no priority slot holds a value. Present only on a commandable object.

How it behaves

The object is commandable only when it has a priority array and a relinquish default. Without them a client writes Present_Value directly. The standard pairs the type with the OUT_OF_RANGE algorithm for intrinsic reporting, and a fault algorithm for out-of-range readings may also apply.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_ANALOG_VALUE build option and add each object with BACnetStack_AddObject. The stack uses the callback you register with BACnetStack_RegisterCallbackGetPropertyReal and the BACnetStack_RegisterCallbackSetPropertyReal callback. It becomes commandable once you enable both PriorityArray and RelinquishDefault; the stack then reads the priority array through the BACnetStack_RegisterCallbackGetPropertyBool callback and the BACnetStack_RegisterCallbackGetPropertyReal callback and does not call the plain Present_Value getter. Arm alarms with BACnetStack_SetIntrinsicOutOfRangeAlgorithm and faults with BACnetStack_SetFaultOutOfRangeAlgorithmReal.

Related object types

Analog Input, Analog Output, Large Analog Value

Properties

The properties ASHRAE 135-2024 clause 12.4 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.
Present_Value	Real	R4	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.
Description	CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	R	yes	no	0
Reliability	BACnetReliability	O	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	R	yes	no	false
Units	BACnetEngineeringUnits	R	yes	no	95 (no units)
Priority_Array	BACnetARRAY[16] of BACnetOptionalReal	O1	no	no	Built by the stack from your callbacks.
Relinquish_Default	Real	O1	no	no	No default: value-not-initialized until a callback or a client write supplies one.
COV_Increment	Real	O2	no	no	0.0
Time_Delay	Unsigned	O3,6	no	no	0
Notification_Class	Unsigned	O3,6	no	no	0
High_Limit	Real	O3,6	no	no	0.0
Low_Limit	Real	O3,6	no	no	0.0
Deadband	Real	O3,6	no	no	0.0
Limit_Enable	BACnetLimitEnable	O3,6	no	no	An empty bit string.
Event_Enable	BACnetEventTransitionBits	O3,6	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O3,6	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O3,6	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O3,6	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	O3,6	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	Real	O	no	no	0.0
Max_Pres_Value	Real	O	no	no	0.0
Resolution	Real	O	no	no	0.0
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Fault_High_Limit	Real	O9	no	no	0.0
Fault_Low_Limit	Real	O9	no	no	0.0
Current_Command_Priority	BACnetOptionalUnsigned	O1	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	O16	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	""