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Doc # E107706 V1.25 5-14
5.11:
RS-4485
Connection—Nexus
Meter
to
Nexus
I/O
Modules
Six feet of RS-485 cable harness is supplied. Insert one end of the cable into Port 4 of the Nexus
1250/1252 Meter.
Insert the other end of the cable into the I/O module’s female RS-485 side port (see Figure 5.9). The
connectors fit only one way into the ports.
Use the male RS-485 side port to attach another I/O module. The Nexus 1250/1252 will power up to
four connected I/O modules using 15–20V DC at 50–200mA, represented by dashed lines in the
figure below. Use the steps below (section 5.12) to determine if you must use a separate power
source (for example, EIG PSIO) to supply added power to the group. RS-485 communication is
viable for up to 4000 feet (1219 meters). However, if your cable length exceeds 200 feet, use the
remote power supply and:
• Connect the A(+) and B(-) terminals on the Nexus to the A(+) and B(-) terminals of the female
RS-485 port. Connect the shield to the shield (S) terminal. The (S) terminal on the Nexus 1250/
1252 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 termination resistors at each end, connected to the A(+) and B(-) lines. RT is
approximately 120 Ohms. NOTE: Refer to section 5.3 for RT Explanation.
+V- S B(-)A(+)
A(+) B(-) S - V +
Figure 5.13: Nexus Meter Connected to Nexus I/O Module
R
T
R
T
Male Side Port on Nexus I/O Module
Nexus Meter Port 4