janitza RCM 202-AB, Руководство пользователя и технические данные

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18
RCM 202-AB
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18 RCM 202-AB
Bus structure
The bus structure of the individual Modbus segments is basically linear. Up to 247
participants can be connected in a Modbus segment. If the data volume of the Mod-
bus participants is too large, the number of participants must be reduced. The cable
is closed with resistors at the start and end of a segment.
Fig. 7: simplified connection diagram of the RS485 interface (example)
Termination resistors
The D
+
/D
-
data line of a Modbus segment must always be provided with a termination
resistor of 120 Ω at the start and end to prevent reflections (termination).
Shielding
Twisted and shielded cable is always used for connections via the Modbus interface
(RS485). For a sufficient shielding effect, the shielding must be connected extensively
to one end of a cable with a grounded housing or cabinet parts.
Connection
The twisted wires of the cable must be connected to terminals “B+” and “A-”. In order
to equalize the potential differences between multiple RCM 202-AB, the ground ter-
minals of all devices on the bus must be connected together. The second twisted wire
pair of the bus cable is used for potential equalization. Both wires must be connected
to each ground terminal. The ground cable from both wires must be connected to one
end of the bus cable with PE.
WARNING
The power supply connection and the transformer connections of the RCM
202-AB may be switched on only after connecting the ground terminal and
grounding the ground cable.
There is a risk of electric shock.