Installation & Operation Manual
- Model VTS
Contents of this Manual are Subject to Change Without Notification
Page 22
SECTION 7
–
OPTIONAL BACNET MS/TP
BACnet® is a standard data communication protocol designed specifically for building
automation and control networks. The Accutrol VTS Transmitter 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.
7.1 BACnet Objects
The Accutrol VTS
Transmitter product family supports a collection of BACnet-visible objects
which are defined in the following table.
Point
Object Description
Present
Value Type
Units
DE ###
Device Instance
Write
###
AI1
Airflow Volume
Read
Volume
AI2
Flash Writes Remaining
Read
Note 1
AV1
Unsubscribed COV Interval
Write
Sec
AV2
Airflow Volume Measurement Adjust
Write
%
BV1
Write to Flash
Write
Note 2
MSI1
Airflow Volume Units
Write
1
= CFM
2
= CMS
3
= CMM
4
= CMH
5
= LPS
6
= LPM
Notes:
1.
The VTS transmitter has an internal counter which limits the number of flash writes
to 10,000. BACnet point AI2 is provided so the number of remaining flash writes
available can be monitored over the BACnet.
2.
Writing a value of (1) to the BACnet Object BV1 will cause the transmitter to copy the
active configuration stored in volatile memory (RAM) and write that value to
nonvolatile memory (FLASH).
3.
Nonvolatile Flash memory has a limited number of Lifetime Write Cycles, therefore
the VTS has an internal limit of 10,000 flash writes to protect the microcontroller
from damage.
