Emerson MultiFlex RTU, Installation And Operation Manual

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8 • MultiFlex RTU Operator’s Guide 026-1706 Rev 3
3 The I/O Network
Although the MultiFlex RTU can operate as a
stand-alone controller, it relies on an Einstein or
REFLECS unit for advanced features such as
remote dial-in/dial-out, logging, and alarm
control. All MultiFlex boards and controllers use
an RS485 network connection to communicate
with Einstein and REFLECS site controllers.
Technicians who are familiar with Emerson’s
previous generation 16AI, 8IO, and ARTC
boards will find the network setup procedure for
the MultiFlex RTU boards to be very much the
same.
3.1. Wiring Types
Emerson specs Belden #8641 shielded twisted
pair cables for use as I/O network wiring (or
Belden #82641 and Belden #88641 for plenum
installations).
If the recommended cable is not available in
your area, be sure the wiring meets or exceeds
the following specs:
3.1.1. Daisy Chains
The RS485 Input/Output (I/O) network connects
all input and output communication boards
together in a single open communications loop.
This loop, or “daisy chain,” connects the
Einstein or REFLECS to multiple input and
output communication boards, and terminates at
the last input or output board on the network. A
diagram of this network arrangement is shown in
Figure 3-1 .
3.1.2. Network ID Numbers
Each device on an RS485 segment has a network
dip switch that must be used to assign the board
a unique network ID number .
The network ID number makes a board unique
from other boards on the network of the same
type. This allows the site controller to find it and
communicate with it easily.
Boards of the same type should be numbered in
sequence, starting with one and continuing with
two, three, and so forth.
Shielded? Yes
Conductor Type Twisted Pair
Gauge 18 - 24 AWG
Capacitance between sig -
nal wires
31 pF/ft or less
Capacitance between sig -
nal and shield
59 pF/ft or less
Nominal Impedance 120

50

Table 3-1 - RS485 I/O Network Wiring Specifications
Figure 3-1 - I/O Network Configurations