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BACnet (Building Automation and Control Networks) defines a set of standard object types that represent various components, devices, or systems in building automation. Each object type contains properties that describe its functionality and enable interaction.
The following diagram shows a BACnet network in the Wattsense environment :
Principle of BACnet scanning
Scanning a BACnet network typically involves discovering devices and their associated objects on the network. BACnet uses the Who-Is and I-Am services for device discovery.
Who-Is Command
This command broadcasts a request to identify all BACnet devices on the network.
Devices on the network will reply with I-Am messages, which typically contain:
- Device Instance ID
- Network Address
- Device Object Name
Query Device Objects
Once devices are identified, a request can be sent to read objects properties.
You can use software tools like Yabe (Yet Another BACnet Explorer) interface to perform these actions:
Launch the tool and configure the network settings (e.g., BACnet/IP port and broadcast address).
Perform a Who-Is broadcast.
View the list of devices responding with I-Am.
Select a device and explore its objects and properties.
BACnet objects
The Wattsense console BACnet scan module can explore and display basic informations (type, name, description) for all kind of objects (BACnet standard ANSI/ASHRAE 135-2020).
Additionally, the properties of multiple objects (supported objects) can be manipulated (read and/or write access). This functionality mainly concerns the Present_Value property.
Here is a listing of supported BACnet objects by Wattsense :
| Object Syntax | Object Name | NameDescription |
| Analog Objects |
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| OBJ_ANALOG_INPUT (0) | Analog Input (AI) | Represents continuous input values like temperature or pressure. |
| OBJ_ANALOG_OUTPUT (1) | Analog Output (AO) | Represents continuous output values like setpoints. |
| OBJ_ANALOG_VALUE (2) | Analog Value (AV) | Represents continuous values used internally or for integration. |
| Binary Objects | ||
| OBJ_BINARY_INPUT (3) | Binary Input (BI) | Represents discrete input states (e.g., open/closed). |
| OBJ_BINARY_OUTPUT (4) | Binary Output (BO) | Represents discrete output states (e.g., on/off). |
| OBJ_BINARY_VALUE (5) | Binary Value (BV) | Represents discrete values used internally or for integration. |
| Multistate Objects |
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| OBJ_MULTISTATE_INPUT (13) | Multistate Input (MSI) | Represents inputs with multiple states (e.g., selector switches). |
| OBJ_MULTISTATE_OUTPUT (14) | Multistate Output (MSO) | Represents outputs with multiple states (e.g., fan speeds). |
| OBJ_MULTISTATE_VALUE (19) | Multistate Value (MSV) | Represents multistate values used internally or for integration. |
| Schedule and Calendar Objects |
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| OBJ_SCHEDULE (17) | Schedule | Represents time-based scheduling of values or events. |
| Other Control and Utility Objects |
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| OBJ_CHARACTERSTRING_VALUE (40) | Character String Value | Represents text data storage or display. |
BACnet properties
Each object contains a list of properties.
Here’s an example of the content for a BACnet Analog Input (AI) object :
| Property Name | Description | Example Value |
| Object_Identifier | A unique identifier for the object within the BACnet device. | AI-1 |
| Object_Name | A human-readable name for the object. | Room Temperature |
| Object_Type | Specifies the type of the object. | Analog Input |
| Present_Value | The current value of the input, typically updated dynamically. | 23.5 °C |
| Description | A textual description of the object. | Temperature sensor in Room 101 |
| Status_Flags | Indicates operational status (in alarm, fault, overridden, out of service). | {FAULT=FALSE, ALARM=FALSE} |
| Event_State | Current state of the object for event reporting purposes. | Normal |
| Out_Of_Service | Indicates if the object is out of service (manually overridden). | FALSE |
| Units | Engineering units associated with the value. | Degrees Celsius |
| Update_Interval | Time interval at which the present value is updated (if applicable). | 1 second |
| Min_Pres_Value | Minimum allowable value for the property Present_Value. | 0.0 °C |
| Max_Pres_Value | Maximum allowable value for the property Present_Value. | 50.0 °C |
| Resolution | Smallest increment detectable or reported by the sensor. | 0.1 °C |
| Reliability | Indicates the reliability status of the object (e.g., No Fault Detected, Sensor Fault). | No Fault Detected |
| COV_Increment (*) |
Change of Value increment that triggers a notification if COV reporting is enabled. | 0.5 °C |
| Time_Delay | Time delay before an event is triggered after a condition is detected. | 5 seconds |
| High_Limit | Upper limit for alarming. | 28.0 °C |
| Low_Limit | Lower limit for alarming. | 18.0 °C |
| Notification_Class | Reference to a notification class object for alarm management. | NC-1 |
| Alarm_Value | Value or range that triggers an alarm. | > 28.0 °C or < 18.0 °C |
| Ack_Required | Indicates if acknowledgments are required for alarms/events. | TRUE |
COV_Increment (*) : this property is not supported by Wattsense.
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