BECKHOFF DK9322-0810-0036 - Manual (Page 3)

TwinCAT
TwinCAT, Building Automation
Application Note DK9322-0810-0036
4. Topologies
Devices can be connected to M-Bus in a strand or star topology. The maximum number of meters per segment is 250. Larger
systems can be formed and cascaded with the aid of repeaters.
Slave
Slave
Slave
Slave
Slave
Slave
Slave Slave
M-Bus
master
Slave
Slave
Slave
Slave
Slave
Slave
Slave
Slave
M-Bus
master
Fig. 1 Possible M-Bus topologies
One of the factors limiting the size of an M-Bus network is the wire cross-section. Wiring of an existing building is very complex
and expensive, which is why in such applications radio solutions with lower infrastructure costs tend to be used.
When configuring an M-Bus topology it should be noted that the plug connectors of the bus cable are not standardized, which
may result in complications if components from different manufacturers are used.
4.1 Laying system, cross-section and cable lengths
The lower the line resistance, the longer the cable can be. However, as a basic rule the cross-section should not be less than
0.5 mm² (#20 AWG). Transmission errors may occur if the maximum cable length is exceeded or if the cable cross-section is too
small. A normal telephone cable of type J-Y(ST)Y n x 2 x 0.8 mm (#20 AWG standard twisted-pair) can be used.
Figure 2 shows the number of M-Bus devices that can be connected in relation to the cable length of the M-Bus.
New Automation Technology Beckhoff 3
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