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Doc # E107706 V1.25 5-16
Figure 5.14: Linking Multiple Nexus Devices in Series
Nexus RS-485 Port
Nexus RS-485 Port
RS-485 to RS-232
Converter (RS-485 Master)
+ V - S B(-) A(+)
+ V - S B(-) A(+)
GND TX- RX- TX+ RX+
R
Up to 31 Nexus 1250/1252 Meters Maximum
5.14:
Linking
Multiple
Nexus
Devices
in
Series
You may connect a total of 31 Nexus 1250/1252 Meters in series on a single bus using RS-485. The
cable length may not exceed 4000 feet (1219 meters). Before assembling the bus, each Nexus Meter
must be assigned a unique address; see the Communicator EXT User Manual.
Connect the A(+) and B(-) terminals of each Nexus Meter. Use jumpers on any RS-485 Master
connected at the end of the chain (see section 5.5).
Connect the shield to the (S) terminal on each Nexus and to the Ground on the RS-485 Master. This
connection 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.
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 or the impedance of the wire.
NOTE: Refer to section 5.3 for RT Explanation.
R
T
Jumpers
+ V - S B(-) A(+)