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9.2.1: Power Source for I/O Modules
The Nexus 1250/1252 will supply power to a limited number (3) I/O MODULES. For more, you
must use an external power source, such as the EIG PSIO (12V). Refer to sections 5.12 and 5.13
to Determine Power Needed. RS-485 communication is viable for up to 4000 feet (1219 meters).
You must also do the following:
1. Connect the A(+) and B(-) terminals on the Nexus to the A(+) and B(-) terminals of the male
RS-485 port. Connect the shield to the shield (S) terminal. 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.
2. Put termination resistors at each end, connected to the A(+) and B(-) lines. RT is ~120 Ohms.
NOTE: Refer to section 5.3 for RT Explanation.
3. Connect a source of power to the front of the module.
Figure 9.3: The PSIO Power Source (Side View)
showing Male RS-485 Side Port
Figure 9.4: Power flow from PSIO to I/O Module
Electro Industries/GaugeTech
1.72"
Doc # E107706 V1.25
SIDE LABEL
TOP LABEL
Figure 9.5: Labels for the
PSIO Power Source
(Labels are Red & White.)
9-4
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