Accumulator

An Accumulator object counts pulses and keeps a running total, the way a utility meter does. It is built to match what the meter’s own display shows, including setting an initial reading when the meter is installed. Devices use it for energy, water and gas metering.

Typical uses

• A kilowatt-hour pulse meter on a building feed
• A water meter that sends one pulse per litre
• A gas meter reading used for billing
• A count of items passing a sensor

Key properties

Property	What it holds
Present_Value	The accumulated count, an unsigned integer. It wraps around at Max_Pres_Value.
Scale	Converts counts into engineering units, so a client can show the real quantity.
Units	The engineering unit of the scaled quantity.
Prescale	Describes a divider in front of the counter, to copy how the physical meter advances.
Max_Pres_Value	The highest value before the count rolls over to zero.
Pulse_Rate	The recent rate of pulses, used for demand figures.

How it behaves

Present_Value is not commandable. For intrinsic reporting the standard pairs this type with the UNSIGNED_RANGE algorithm, using High_Limit and Low_Limit. The standard also allows a fault algorithm for out-of-range readings.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_ACCUMULATOR build option and add each object with BACnetStack_AddObject. Present_Value is unsigned, so the stack reads it through the callback you register with BACnetStack_RegisterCallbackGetPropertyUnsignedInteger. Arm the alarm with BACnetStack_SetIntrinsicUnsignedRangeAlgorithm, after BACnetStack_SetAlarmsAndEventsForObjectEnabled. The stack has no fault out-of-range setter for this type: BACnetStack_SetFaultOutOfRangeAlgorithmReal refuses it.

Related object types

Pulse Converter, Analog Input, Positive Integer Value

Properties

The properties ASHRAE 135-2024 clause 12.61 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	Unsigned	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	0
Out_Of_Service	Boolean	R	yes	no	false
Scale	BACnetScale	R	yes	no	No default: the read fails.
Units	BACnetEngineeringUnits	R	yes	no	95 (no units)
Prescale	BACnetPrescale	O	no	no	No default: the read fails.
Max_Pres_Value	Unsigned	R	yes	no	0
Value_Change_Time	BACnetDateTime	O2	no	no	No default: the read fails.
Value_Before_Change	Unsigned	O2,3	no	no	0
Value_Set	Unsigned	O2,3	no	no	0
Logging_Record	BACnetAccumulatorRecord	O	no	no	No default: the read fails.
Logging_Object	BACnetObjectIdentifier	O	no	no	No default: the read fails.
Pulse_Rate	Unsigned	O1,4,7	no	no (yes while Out_Of_Service is true)	0
High_Limit	Unsigned	O4,6	no	no	0
Low_Limit	Unsigned	O4,6	no	no	0
Limit_Monitoring_Interval	Unsigned	O4,7	no	no	0
Notification_Class	Unsigned	O4,6	no	no	0
Time_Delay	Unsigned	O4,6	no	no	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	O6,8	no	no	false
Time_Delay_Normal	Unsigned	O6	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O9	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Fault_High_Limit	Unsigned	O10	no	no	0
Fault_Low_Limit	Unsigned	O10	no	no	0
Audit_Level	BACnetAuditLevel	O11	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O11	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	""