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Installation
3.5 Topology
3.5.1 Topology Types
The BACnet/IP MCA 125 option features a built-in Ethernet
switch with 2 Ethernet RJ45 connectors. Where the
enclosure protection rating if higher than IP2x, the
frequency converter may be equipped with two M12
connectors instead.
The module enables the connection of several BACnet/IP
options in a line topology as an alternative to a traditional
star topology.
The 2 ports are equal. If only 1 connector is used, either
port can be used.
3.5.1.1 Star Topology
Illustration 3.2 Star Topology
3.5.1.2 Line Topology
In many installations, line topology enables simpler cabling
and the use of smaller or fewer Ethernet switches. The
BACnet/IP interface supports line topology with its 2 ports
and built-in Ethernet switch.
When line topology is used, take precautions to avoid
timeout in the BMS when more than 8 frequency
converters are installed in series. Each frequency converter
in the network adds a small delay to the communication
due to the built-in Ethernet switch. When the update time
is too short, the delay can lead to a timeout in the BMS.
MG92K102
Installation Guide
Set the update time as shown in Table 3.1. The numbers
given are typical values and can vary from installation to
installation.
Numbers of frequency converters
connected in series
Table 3.1 Minimum Update Time
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Illustration 3.3 Line Topology
NOTICE
In line topology, activate the built-in switch by powering
all frequency converters, either by mains or a 24 V DC
option card.
NOTICE
Installing frequency converters of different power sizes in
line topology may result in unwanted power-off behavior
when using control word timeout (parameter 8-02 Control
Word Source to parameter 8-06 Reset Control Word
Timeout). Mount the frequency converters with the
longest discharge time first in the line topology. In
normal operation, the frequency converters with bigger
power sizes have a longer discharge time.
Danfoss A/S © 05/2016 All rights reserved.
Minimum update time [ms]
<8
8–16
16–32
>32
Large jitter can occur.
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2
4
8
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3
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