Output Wiring
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RFT9739 Rack-Mount Transmitter Instruction Manual
55
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5.9
RS-485 multidrop network
The RFT9739 can be configured to communicate for any one of the
following options:
• HART protocol over the RS-485 standard
• HART protocol over the Bell 202 standard
• Modbus protocol over the RS-485 standard
• Modbus protocol over the RS-485 standard and HART protocol over
the Bell 202 standard
For communications configuration instructions, see "Communication
configuration mode," page 61. For Bell 202 network wiring, see
Section 5.10, page 56.
Multiple transmitters can participate in an RS-485 multidrop network that
uses HART or Modbus protocol.
• Under HART protocol, an almost unlimited number of transmitters can
participate in the network. Each transmitter must have a unique tag
name. If polling addresses are used, up to 16 transmitters can have
unique polling addresses from 0 to 15.
• Under Modbus protocol, up to 15 transmitters can participate in the
network. Each transmitter must have a unique polling address from
1 to 15.
To connect the transmitter to an RS-485 network, use transmitter
terminals CN2-Z22 and CN2-D22. Figure 5-29, page 56, shows how to
connect one RFT9739 or multiple RFT9739 transmitters to a host
controller for RS-485 serial communication.
• Install twisted-pair, shielded cable, consisting of 24-gauge (0.3 mm²) or
larger wire, between the RFT9739 and an RS-485 communication
device. Maximum cable length is 4000 feet (1200 meters).
• Some installations require a 120-ohm, ½-watt resistor at each end of
the network cable to reduce electrical reflections.
For information on communication protocol requirements for
implementing an RS-485 network, phone the Micro Motion Customer
Service Department:
• In the U.S.A., phone 1-800-522-6277, 24 hours
• Outside the U.S.A., phone 303-530-8400, 24 hours
• In Europe, phone +31 (0) 318 549 443
• In Asia, phone 65-770-8155
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