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7000 Bus Converter User Manual (version 1.2,Feb/2003, 7PH-006-10) --------------- 75
For example, the 7510, 7510, 7510 are used to isolate local
modules from RS-485 network. If there is high energy transient on
RS-485 network, all the local modules will be safe.
Isolation Configuration (Strongly Recommended)
If the RS-485 network is not over 100 meters, the terminated
resistors are not needed. However, it may be necessary to insert two
terminated resistors at both end of the RS-485 segment. It is not easy to
calculate the value of a terminator resistor. The best way to do this is to
use an oscilloscope to check the RS-485 signal directly. If the impedance
match of RS-485 network is OK, the oscilloscope will show a very nice
square wave. If these square wave signals are distorted, the user will
need to insert two terminators at both end of the RS-485 segment.
R
T
Host
PC
PLC
D+
D+
7xxx
7510
7520
7510
D- D-
GND
7xxx
7xxx
7xxx
7xxx
7xxx
Is terminator
7xxx
7xxx
Group A
Group B
RS-485
RS485
RS-485
RS232 RS485
RS485
7510
7510
RS485
RS485 RS485
RS485 RS485RS485
Group C
OK
Resistor value o
f
terminator is too small
Resistor value o
f
terminator is too big