Relay MR005DL User Manual page 8

Planning M-Bus networks:
Two effects must be considered before projecting M-Bus networks:
1. The signals must not be distorted to much by the influence of the capacitance of the
cable. The capacitance of the network depends on the length of the network, this means
the total sum of cable length. Lower baudrates allow a higher bus capacity.
2. Each meter must be supplied by the M-Bus with a minimum voltage of 24V. The voltage
drop on the bus line is caused by the transmit current of the communicating slave of up
to 20mA, the supply current of the slaves in the respective bus segment, the internal
resistance of the M-Bus master, the resistance of the cable and the connection
resistances of the joints. The distance between a slave and the master is inverse
dependent on the number of slaves in this segment and on the cable diameter.
The maximum allowed resistance of the cable can be estimated:
The calculation for a standard phone cable
following values:
Baudrate
Max. total cable length (@150nF/km):
No. of unit loads in the
respective segment
There are remote repeaters (our art.no. DR007 or PW250) available for extending the network
length and the number of connected slaves. Cascading these remote repeaters allows a nearly
unlimited bus extension. The place in which a remote repeater is placed must provide a mains
supply.
Shielding
Tests showed the result that a shielding of the M-Bus cable is not necessary. Please avoid a
connection between any of the bus lines to the shielding or protective ground.
User Manual MR005FA+DL / MR006FA+DL ·04/2018 · VERSION 1.4
Equally distributed
3
20
MR005FA+DL / MR006FA+DL
(75/km, 150nF/km) presents the
JYSTY nx2x0.8
9600 Baud 2400 Baud
1 km 4 km
Max. distance to the meter (@75/km)
slaves at end of cable
4.0 km
2.5 km
300 Baud
12 km
4.0 km
1.5 km
8