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M-Bus Master MultiPort 250D
In big networks using secondary addressing, worst case
load must be considered as 250 slaves of 1 UL (Unit Load)
each drawing 5.4 A, which thin cables will not be able to
withstand.
Measurement of loop resistance.
Please note that resistance can be stated in two different
ways in cable specifications, i.e. as cable resistance or as
loop resistance.
Loop resistance is the total resistance measured through
the two conductors. Cable resistance is the resistance
through one conductor. Therefore, loop resistance is
Measurement of cable resistance.
always twice the cable resistance.
4.3.2
Cable topology
An M-Bus network normally uses bus or star topology or a combination of both.
The advantage of bus topology is shorter wires. The disadvantage is that a cable interrupt will mean that all the
following meters can no longer be read.
The advantage of star topology is the fact that all the other meters can still be read after a cable interrupt. The
disadvantage is a large consumption of cable with a high leading load, which reduces the maximum cable length and
makes a reduction of communication speed necessary, respectively.
Bus topology offers two solutions. One solution is to loop the cable through each meter. This solution presupposes that
there is room for two cables and that the connection terminals are prepared for the connection of two sets of cables. All
connections are thereby typically made inside the meter.
The other solution is to use bus topology with each individual meter connected to the bus. With this solution, a number
of connections must be established on the bus itself.
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Kamstrup A/S • 5512853_C1_GB_01.2017
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