User Manual
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Building Technologies M-bus System CE1P5361en
HVAC Products 5 Engineering 08.02.2007
5.4.5 Sizing
In each M-bus segment, it must be ensured that the required minimum bus voltage is
available for all M-bus devices (slaves) and that the required rate of data transmission
is observed.
The table below contains a number of basic application examples for which a detailed
analysis of the bus voltage and of the rate of data transmission is not required.
Type of plant
Maximum
distance
Total cable length
Dia. / cross-
sectional area
Number of M-bus
devices (slaves)
Maximum rate of
transmission
Smaller residential
buildings
350 m 1000 m 0.8 mm 250 9,600 Baud
250 2,400 Baud Larger residential
buildings
350 m 4000 m 0.8 mm
64 9,600 Baud
Smaller town sections 1000 m 4000 m 0.8 mm 64 2,400 Baud
Larger town sections 3000 m 5000 m 1.5 mm
2
64 2,400 Baud
Village, town section 5000 m 7000 m 1.5 mm
2
16 300 Baud
Point-to-point connection 10,000 m 10,000 m 1.5 mm
2
1 300 Baud
Each M-bus device (slave) is powered via M-bus and, therefore, produces a volt-
age drop on the bus cables
For all M-bus devices (slaves) at the final points of an M-bus segment, the mini-
mum bus voltage must be checked
The voltage drop down to the final points is determined by the type of cable and
the number, distance and arrangement of the connected M-bus devices (slaves)
For calculating the voltage drop down to the final points (T), the M-bus devices
(slaves) on the side branches are mapped on the branch to be calculated. The
voltage drop on the side branches is of no importance to the branch to be calcu-
lated
2
3
2
3
T
T
5361Z23
M--bus devices (slaves) on the branch to be calculated
When using cable length charts, it is not necessary to calculate the voltage drop. The
charts show
the maximum cable length to the final point depending on the cross-sectional area
the number of connected M-bus devices (slaves)
Note: The SONOHEAT
®
heat meters with an M-bus module up to V1.06 produce a
bus load of 1.5. A SONOHEAT
®
heat meter with an M-bus module up to V1.06 cor-
responds to 1.5 devices. All other devices and SONOHEAT
®
heat meters with an
M-bus module of V2.01 or higher correspond to 1 bus load.
For additional charts, refer to section 7.4 "Cable length charts".
Quick reference
Minimum bus voltage
Cable length charts