Instruction manual

Output Wiring
continued
RFT9739 Field-Mount Transmitter Instruction Manual 47
Output Wiring Startup TroubleshootingBefore You Begin Getting Started Mounting
Power-Supply and
Sensor Wiring
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
settings," page 9. For Bell 202 network wiring, see
Section 5.10
,
page 48.
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 247 transmitters can participate in the
network. Each transmitter must have a unique polling address from
1 to 247.
To connect the transmitter to an RS-485 network, use RFT9739
terminals 27 and 26.
Figure 5-22
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 AWG (0.25 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 both ends 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 [phone], 24 hours
• Outside the U.S.A., phone [phone], 24 hours
• In Europe, phone [phone]
• In Asia, phone [phone]