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System /
application
2
5
L1
L2
L3
4-wire
N
3-phase
asymmetric
2
5
load
u
x
X
U
L1
L2
L3
N
2
8
4-wire
3-phase
asymmetric
L1
load,
L2
Open Y
L3
connection
N
Low-voltage system
6. Connecting devices to the bus
The RS 485 interface of the DME 401 is galvanically isolated
from all other circuits. For an optimal data transmission the
devices are connected via a 3-wire cable, consisting of a
twisted pair cable (for data lines) and a shield. There is no
termination required. A shield both prevents the coupling of
external noise to the bus and limits emissions from the bus.
The shield must be connected to solid ground.
You can connect up to 32 members to the bus (including
master). Basically devices of different manufacturers can be
connected to the bus, if they use the standard MODBUS
protocol. Devices without galvanically isolated bus interface
are not allowed to be connected to the shield.
All manuals and user guides at all-guides.com
Measuring inputs
8
1
4
6
11
3
7
8
11
1
3
4
6
7
u
u
x
x
X
X
k
l
k
l
U
U
K
L
k
K
L
K
11
1
3
4
6
7
9
k
l
k
l
K
L
k
l
K
L
K
L
Terminals
9
2
5
L1
L2
L3
N
9
l
3 single-pole insulated voltage transformers
L
in high-voltage system
1
u
u
x
x
k
X
X
U
U
L1
K
L2
L3
N
2 single-pole insulated voltage transformers
in high-voltage system
The optimal topology for the bus is the daysi chain connection
from node 1 to node 2 to node n. The bus must form a single
continuous path, and the nodes in the middle of the bus must
have short stubs. Longer stubs would have a negative impact
on signal quality (reflexion at the end). A star or even ring
topology is not allowed.
There is no bus termination required due to low data rate. If
you got problems when using long cables you can terminate
the bus at both ends with the characteristic impedance of the
cable (normally about 120 Ω). Interface converters RS 232 ⇔
RS 485 or RS 485 interface cards often have a built-in
®
termination network which can be connected to the bus. The
second impedance then can be connected directly between
the bus terminals of the device far most.
8
1
4
6
9
11
3
7
k
l
k
l
K
L
k
l
K
L
K
L
3
4
5
6
7
8
9 11
2
k
k
l
l
l
L
L
K
L
K
L
29
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