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14_ installation and external connection
installation and external connection
EARTH-GROUNDING THE COMMUNICATION CABLES
We recommend you to use a proper grounding system for the communication cables.
The best grounding method is to earth-ground the shield wire of the communication cable. However, the earth-grounding
of the communication cable is not easy at all, and it also causes an increased installation cost. There are three grounding
points available for installation:
1. Earth Ground
2. Chassis Ground
3. Power Ground
The most important thing about the earth-grounding lies in connecting neither end of the shield wire to the grounding
system simultaneously. This will cause a current fl ow through the shield wire when the voltage level of both ends of the
shield wire is not equal and this current fl ow will introduce some noise and interference to communications.
It is recommended to connect ONLY one end of the shield wire of the communication cable to the grounding system. If
you can locate an earth grounding point nearby, connect one end of the shield wire to that point. If you could hardly locate
an earth grounding point nearby, connect one end of the shield wire to the chassis ground point. If you could locate
neither of an earth or chassis grounding point nearby, connect one end of the shield wire to the power ground point
(GND). Note that if the chassis is not properly earthed and fl oated from the ground level, then grounding communication
cable to the chassis will produce the worst communication. If this is the case, use the power ground point rather than the
chassis ground.
HOST PC
Earth Ground
or Chasis Ground
or Power Ground
RS-232
RS-422/RS-232
Converter
RS-422
RS-422 RS-422 RS-422
GND
#1
GND
#2
GND
#3
GND
#n
Communication
Wires
RS-422 Cable
Connect
ShieldWire
Open