Analog Input

An Analog Input object models a measured value from a sensor, such as a temperature or a pressure. The device reads the sensor and reports the number. Clients read it, subscribe to changes and can set alarms on it.

Typical uses

• A room temperature sensor
• A duct static pressure transmitter
• An outdoor humidity reading
• A current transformer reporting amperes

Key properties

Property	What it holds
Present_Value	The current measurement, a real number. Clients read it and usually subscribe to it.
Units	The engineering unit of the value, such as degrees Celsius or pascals.
COV_Increment	The smallest change in Present_Value that triggers a change-of-value notification to subscribers.
High_Limit	The upper edge of the normal band for alarms. Low_Limit is the lower edge.
Deadband	How far the value must return inside a limit before the alarm clears.

How it behaves

Present_Value is not commandable. Subscribers receive change-of-value notifications once the value moves by COV_Increment. 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_INPUT build option and add each object with BACnetStack_AddObject. The stack reads Present_Value through the callback you register with BACnetStack_RegisterCallbackGetPropertyReal. Arm alarms with BACnetStack_SetIntrinsicOutOfRangeAlgorithm after BACnetStack_SetAlarmsAndEventsForObjectEnabled, and fault detection with BACnetStack_SetFaultOutOfRangeAlgorithmReal.

Related object types

Analog Output, Analog Value, Averaging

Properties

The properties ASHRAE 135-2024 clause 12.2 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	R1	yes	no (yes while Out_Of_Service is true)	No default: value-not-initialized.
Description	CharacterString	O	no	no	""
Device_Type	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
Update_Interval	Unsigned	O	no	no	0
Units	BACnetEngineeringUnits	R	yes	no	95 (no units)
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
COV_Increment	Real	O2	no	no	0.0
Time_Delay	Unsigned	O3,5	no	no	0
Notification_Class	Unsigned	O3,5	no	no	0
High_Limit	Real	O3,5	no	no	0.0
Low_Limit	Real	O3,5	no	no	0.0
Deadband	Real	O3,5	no	no	0.0
Limit_Enable	BACnetLimitEnable	O3,5	no	no	An empty bit string.
Event_Enable	BACnetEventTransitionBits	O3,5	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O3,5	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O3,5	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O3,5	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O5	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O5	no	no	""
Event_Detection_Enable	Boolean	O3,5	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O5	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O5,6	no	no	false
Time_Delay_Normal	Unsigned	O5	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O7	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Interface_Value	BACnetOptionalReal	O	no	no	Null
Fault_High_Limit	Real	O8	no	no	0.0
Fault_Low_Limit	Real	O8	no	no	0.0
Audit_Level	BACnetAuditLevel	O9	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O9	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	""