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7000 Bus Converter User Manual (version 1.2,Feb/2003, 7PH-006-10) --------------- 24
In most applications, the 7520 are used to convert the RS-232 signal to
RS-485 network. Normally the 7520 does not use the same DC power
ground as the Host PC/PLC, and the isolation site is in the RS-232 section.
Therefore the Host PC/PLC is isolated from RS-485 network. That is to say,
if there is any high voltage transient on RS-485 network, the Host PC/PLC
will be free from damage.
WARNING!! ERROR CONDITION 1: if the 7520 are replaced by 7520R and
the 7520R uses the same DC power ground with 7000. In this situation,
(1) The Host PC/PLC is common ground with RS-232
(2) The RS-232 is common ground with power ground of 7520R
(3) The power ground of 7520R is common ground with power ground of
7000
(4) The power ground of 7000 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. The Host PC/PLC may be damaged if there is high voltage transient
on RS-485 network.
7520
7000 situation
RS-485
RS-232
Host PC/PLC
Note: the power ground o
f
7000 and RS-485 is
common ground.
This is the same for Adam
4000, Nudam 6000 and
DATAFORTH 9B series
modules.