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7000 Bus Converter User Manual (version 1.2,Feb/2003, 7PH-006-10) --------------- 25
WARNING!! ERROR CONDITION 2: if the 7520 uses the same DC
power ground with Host PC/PLC (for example, Host PC/PLC
provide non-isolated DC power source to 7520). In this situation,
(1) The Host PC/PLC is common ground with power ground of 7520
(2) The power ground of 7520 is common ground with RS-485
Therefore the Host PC/PLC is common ground with RS-485 network.
That is to say, there is no isolation between Host PC/PLC and RS-485
network. So the Host PC/PLC may be damaged if there is high voltage
transient on RS-485 network.
OK CONDITION: If the DC power ground of 7520 or 7520R is not common
to any module, the Host PC/PLC will be isolated from RS-485 network in
all conditions.
The power adapter PWR-24 is designed for single 7000 series modules
only. The 24V DC output of the PWR-24 is isolated from its AC input. If the
7520 or 7520R is connected to the PWR-24, this PWR-24 cannot connect
to the other module. Normally the Host PC/PLC uses a switching power and
the DC output of this power supply is also isolated from its AC input. Therefore
the DC power ground of 7520 or 7520R is isolated from Host PC/PLC.
Therefore, the Host PC/PLC is isolated from RS-485 network in all condition.
7520
7520R
Host PC/PLC
RS-485
RS-232
7000 series
7000 series
Connecting 256
modules without
repeater, 7510
PWR-24
Host PC/PLC is isolated
from RS-485 network
for 7520 or 7520R in
all condition