The BACnet Object

BACnet object(s) are concepts that allow the communication and organization of data related to inputs, outputs, software, and calculations to be performed. The BACnet Object can manifest itself in a variety of ways. These ways include:

  • Single Points
  • Logical Groups
  • Program Logic
  • Schedules
  • Historical Data

The BACnet object covers both physical and non-physical concepts. For example, a thermostat could be considered a physical concept and the HVAC system as the output device. A HVAC maintenance schedule in the form of software is an example of a non-physical concept.

All BACnet objects contains properties for information exchange and commands. One could view these properties in a tabular format with two columns. The first column lists the property name, and the second column gives a property value. Information in the second column can exist in read-only or write-enable format.

The following is a BACnet object example of an analog input for a space temperature sensor in a building:

Object Name Space Temp
Object Type Analog Input
Present Value 71
Status Flags Normal, InService
High Limit 77
Low Limit 67

The first four properties in the table are required by the BACnet standard. The last two properties are considered optional. These optional objects are often required by a developer, but that object must conform to the BACnet standard. The example shows only a few of the properties with an object. In the real-world, especially in a building automation setting many more properties would be present in the object.

Most experts and sources indicate there are 23 standard BACnet objects used in building automation systems. Standard objects are those objects that operate within the BACnet standard.

  • Binary Input
  • Binary Output
  • Binary Value
  • Analog Input
  • Analog Output
  • Analog Value
  • Averaging
  • LifeSafety Zone
  • LifeSafety Point
  • Multi-State Input
  • Multi-State Output
  • Multi-State Value
  • Loop
  • Calendar
  • Notification Class
  • Command
  • File
  • Program
  • Schedule
  • Trend Log
  • Group
  • Event Enrollment
  • Device

This list of 23 standard objects is representative of those functions in building automation and control systems of the present day.

Written by: Scott Cosby

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© Chipkin Automation Systems 2007