Installation & Operation Manual - Model AVC4000
Contents of this Manual are Subject to Change Without Notification
Page 31
SECTION 7
–
BACnet
BACnet® is a standard data communication protocol designed specifically for building
automation and control networks. The AVC controller uses the BACnet MS/TP (Master-
Slave/Token Passing) protocol which is a type of MAC layer implemented using the EIA-485
signaling standard. The performance of the MS/TP network is heavily influenced by the
network traffic load, the assignment of MS/TP node addresses and the network configuration
parameter
Nmax_info_frames
. Additionally, it is imperative the physical network layer is
properly configured (cabling, EOL terminations, bias, etc...) and is verified to be reliable
otherwise the network performance can be compromised. Due to the complexities associated
with network communications, the most reliable method for communicating the airflow set
point to the AVC controller is via Analog Signal.
7.1 BACnet Objects
The AVC AccuValve supports a collection of BACnet-visible objects. In addition to a Device
object whose instance is programmed by writing to the current Object_Identifier or the
“wildcard”
Object_Identifier whose instance is 4194303, the AVC supports several standard
object types as described herein. The following table defines the visible objects. The PV column
indicates whether the Present_Value is Read Only
“R”
, Writable
“W”
or a Commanded
“C”
point.
The standard objects; DEV, AI, AV, AO, BI, BV, and MSI support required properties for those
object types. Object_Name is writable with provision for 64-character maximum length names.
BI Inactive_Text and Active_Text, and MSI State_Text are writable.
Each AI/AV/AO object’s Units property automatically changes to the appropriate unit for US or
SI measurement based on the value of MSI3 and MSI4. Internally Present_Values are stored in
US units and converted to/from SI units only when read or written.
Standard object property values other than Present_Value shall be derived as follows:
Object_Identifier: generated automatically from request
Object_Type: generated automatically from request
Object_Name: writable
Polarity: always NORMAL
Units: Reference Table above, MSI3 and MSI4
State_Text, Inactive_Text: Active_Text writable
Status_Flags: always {FALSE,FALSE,FALSE,FALSE}
Event_State: always NORMAL
Out_Of_Service: always FALSE
The internal Airflow Control loop dictates the Airflow Actuator Position (AO1) at a priority of 10.
Devices external to the AVC that need to control the actuator directly shall use higher priority
levels (9, 8, 7 etc.).
Objects; AI, AV, and AO shall support the COV_INCREMENT property which shall also be
writable.
