Electro Industries/GaugeTech Nexus 1250, Installation & Operation Manual

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Electro Industries/GaugeTech
Doc #: E107-7-06-121
5-10
5.7: RS-485 Connection 5.7: RS-485 Connection— —Nexus to an RS-485 Master (Unicom or Modem Nexus to an RS-485 Master (Unicom or Modem
Manager) Manager)
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To establish communication between a Nexus Monitor and any RS-485 master, such as EIG’s
Unicom 2500, Modem Manager or other RS-232–485 converter, use a shielded, twisted pair cable.
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Use an RS-485 port (Ports 1–4) on the Nexus Monitor. If you use Port 1, set the selector switch
beneath it to RS-485 (see Figure 5.3). Connect the A(+) and B(-) terminals on the Nexus to the (+)
and (-) terminals on the master. Provide jumpers on the master, linking its two (-) terminals and two
(+) terminals. RS-485 communication is capable for up to 4000 feet (1219 meters).
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Connect the shield to the Ground (G) terminal on the Master. The (S) terminal on the Nexus is used
to reference the Nexus port to the same potential as the source. It is not an earth ground connection.
You must also connect the shield to earth-ground at one point.
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Provide resistors at each end, connected to the (+) and (-) lines. RT is approximately 120 Ohms, but
this value may vary based on length of cable run, gauge and the impedance of the wire.
Port on RS-485 Master
– – + + G
+ V - S B(-) A(+)
Figure 5.9: Nexus Monitor Connected to an RS-485 Master
Port on Nexus Monitor
RT
RT
Courtesy of NationalSwitchgear.com