Micro Motion Fisher-Rosemount RFT9709, Инструкция по эксплуатации

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20
RFT9709 Transmitter Instruction Manual
Wiring
continued
RS-485 output The RS-485 physical layer is used for serial communication with the
HART or Modbus protocol. Multiple transmitters can participate in an
RS-485 multidrop network.
• Under HART protocol, up to 32 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.
• Configuration switches on the RFT9709 allow the choice of Bell 202 or
RS-485 physical layers for HART or Modbus communications. Make
sure switches are set as instructed in Section C.2, page 47, before
attempting to use the RFT9709 in an RS-485 multidrop network.
Figure 2-12 shows how to connect one transmitter or multiple
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 RFT9709 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.
Figure 2-12. RS-485 wiring
A
B
A
B
15
16
15
16
15 16
RFT9709
RFT9709
RFT9709
15 16
RFT9709
One RFT9709 and
a host controller
Multiple RFT9709s and
a host controller
Host
controller
Host
controller
120 ohm 1/2 watt
(if required – see note)
Note:
For long-distance communication, or if
noise from an external source interferes
with the signal, install 120-ohm ½-watt
resistors across terminals of both end
devices.
120 ohm 1/2 watt
(if required – see note)
120 ohm 1/2 watt
(if required – see note)
120 ohm 1/2 watt
(if required – see note)
09wire.fm Page 20 Monday, March 1, 1999 4:31 PM