User Manual

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Building Technologies M-bus System CE1P5361en
HVAC Products 5 Engineering 08.02.2007
0
500
1000
1500
2000
2500
3000
3500
4000
10
20 40 60
80
100 120 140 160 180 200 220 240
n
5361D02
l [m]
Cable lengths based on a cable diameter of 0.8 mm
l Cable length [m]
n Number of M-bus devices
Maximum cable length with equidistant distribution of the M-bus devices (slaves)
Maximum cable length if all M-bus devices (slaves) are connected to the end of the cable
Same as ; communication works in spite of a short-circuit on one of the M-bus devices (slave )
(M-bus component TSS721)
For calculation formulas for the voltage drop, refer to EN 1434-3.
 The total of all cable lengths, the connected M-bus devices and protection devices
produce capacitance in the M-bus segment. This capacitance restricts the rate of
data transmission.
C
Segment
= C
Master
+ C
Cable
+ n × C
Slave
+ k × C
Protection
C
Segment
Total capacitance in the M-bus segment
C
Master
Initial capacitance of M-bus master = 200 nF
C
Cable
Cable capacitance = total cable length l × capacitance per unit length
(typically, e.g. cable J-Y(St)Y 2 × 2 × 0.8: C
Cable
= l × 120 nF/km)
C
Slave
Input capacitance of M-bus devices (slaves) = 0.5 nF
n Number of M-bus devices (slaves)
Note: The SONOHEAT
®
heat meters with an M-bus module up to V1.06 correspond to a bus
load of 1.5. A SONOHEAT
®
heat meter with an M-bus module up to V1.06 corresponds to1.5
devices. All other devices and SONOHEAT
®
heat meters with an M-bus module of V2.01 or
higher correspond to 1 bus load
C
Protection
Input capacitance of protection devices (type 1: 2.3 nF; type 2: negligible)
k Number of external protection devices
 The maximum rate of data transmission per M-bus segment can be determined
with the help of the following table
Total capacitance of M-bus segment Maximum rate of data transmission
Up to 382 nF 9,600 Baud
Up to 1528 nF 2,400 Baud
Up to 12222 nF 300 Baud
 The lowest of all maximum rates of data transmission of the M-bus segments de-
termines the maximum rate of data transmission in the entire M-bus system
Maximum rate of data
transmission