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BACnet IP/MSTP VAV Controller - INSTALLATION
INSTRUCTION
Termination Resistors
Matched terminating resistors are required at each end of a
segment bus wired across (+) and (-). Use matched precision
resistors rated ¼ W ±1% / 80 - 130Ω.
Ideally, the value of the terminating resistors should match the
rated characteristic impedance of the installed cable. For
example, if the installed MS/TP cable has a listed characteristic
impedance of 120Ω, install 120 Ω matched precision resistors.
Shied Termination
Following proper MS/TP cabling shield grounding procedures is
important to minimize the risk of communication problems and
equipment damage caused by capacitive coupling. Capacitive
coupling is caused by placing MS/TP cabling close to lines
carrying higher voltage. If shielding is used, the shielding of each
individual bus segment should be separately connected at one
end to earth.
NOTE:
NOTE:
If any of the devices are electrically isolated, it is
recommended that those devices be connected to signal
ground.
Connecting to BACnet MS/TP Buses
The controller communicates via its BACnet MS/TP interface
with other BACnet MS/TP-capable devices (for example, other
room controllers or MS/TP controllers). In doing so, the
following considerations should be taken into account.
—
Maximum BACnet MS/TP bus length (= "L" on
See
Table 6, "Baud rate vs. Maximum cable length," on
page 15
.
—
Twisted-pair cable, for example,
• AWG 18
• J-Y(ST)Y 4 x 2 x 0.8 mm2 or a special RS485 cable.
• CAT 5,6,7 cable – use only one single pair for one bus
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PLANT
C ONTROLLER
31-XXXX-XX
Figure. 12 .
L*
MSTP VAV
C
ONTROLLER
#1
*for Maximum BACnet MS/TP bus length refer table Baud rate vs. Maximum cable length
Figure 12. Connection to a BACnet MS/TP Bus
16
Prelim Draft - Brand Neutral
• Belden 9842 or 9842NH and
• Daisy-chain topology.
—
Must conform to TIA/EIA RS485 cabling guidelines and
ANSI/ASHRAE Standard 135-2010.
BACnet MS/TP Limitataions
There are two limitations regarding the number of
controllers per BACnet MS/TP channel:
PHYSICAL LIMITATION:
32 loads as per TIA/EIA-485 standard. One BACnet MSTP VAV
controller represents 1/8 load. The physical limitation is
important in case 3rd party devices representing a full load are
connected.
AUTOMAC LIMITATION:
See
Table 8, "MAC Address," on page 16
maxmaster value. It can be modified by the user. Refer IRM
Engineering Tool User Guide - 31-00282 for more information
on how to do this.
A maxMaster of 127 means we can support a maximum of 125
BACnet MSTP VAV controllers, one supervisor, and one BACnet
client (tool) per BACnet MS/TP channel.
Thus, depending upon the actual performance needs and
required communication rates, it is recommended to connect a
smaller number of BACnet MS/TP devices per channel.The
recommendation is not to have more than 62 controllers on
single MSTP channel.
Table 8. MAC Address
Default
maxmaster
Brand
CentraLine
64
1
Webs
127
1
HBS
35
1
MSTP VAV
C
ONTROLLER
#2
for default
Default
Default
Default
MinMAC
MaxMAC
Baud rate
60
38400
127
76800
30
38400
MSTP VAV
C ONTROLLER #..N
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