User Manual
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Building Technologies M-bus System CE1P5361en
HVAC Products 5 Engineering 08.02.2007
peaters, cable routing and the type of cable. Normally, this is an iterative process where
a first approach is made followed by checking. Then, if required, adjustments are made.
1. Prepare a plant diagram:
First, enter all M-bus devices and all distances in the diagram.
2. Select the cable routing:
If cable routing is not specified, it should be chosen such that distances will be as
short as possible. It should be taken into consideration that star-like cable routing
offers advantages when making fault analyses and uses shorter distances between
signal converters or repeaters and M-bus devices. Line topology, by contrast, re-
quires less cable. Normally, optimal cable routing is a mixture of star and line to-
pologies (tree topology).
3. Determine the number of central units, signal converters and repeaters and select
their locations:
Based on the number of M-bus devices used, the minimum number of M-bus cen-
tral units required (refer to section 5.3 "Calculation of the required number of M-bus
central units"), signal converters and repeaters are determined. The central units,
signal converters and repeaters are entered in the plant diagram, choosing possi-
ble locations.
4. Check the approach:
The approach must be checked for each M-bus segment. Two criteria must be ob-
served (refer to subsection 5.4.5 “Planning process”):
Minimum bus voltage at the M-bus devices (slaves)
Maximum rate of transmission
5. Adjust the approach:
If checking the approach reveals that the permissible limits per M-bus segment are
not observed, the M-bus segment must be newly sized. The following readjust-
ments are possible:
Subdivision of individual M-bus segments by means of repeaters
Relocation of signal converters or repeaters
Increase of the cross-sectional area of the bus cable
Change of system topology (e.g. star topology in place of line topology, or vice
versa)
Combination of several pairs of lines
Then, the approach must be checked again (back to point 4.).
Procedure