Emerson IFT9701 - Manual (Page 31)

Model IFT9701 Transmitter Instruction Manual 23
Power Supply and Output Wiring continued
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4.4.2 Milliamp output connected to Bell 202 multidrop network
Devices in a Bell 202 multidrop network communicate by sending and receiving signals to and from
one another. HART protocol supports up to 15 transmitters in a Bell 202 multidrop network.
Other Rosemount SMART FAMILY transmitters can also participate in a HART-compatible network.
• A Bell 202 multidrop network uses twisted-pair wire, and allows only digital communication.
• A HART Communicator or other HART-compatible control system can communicate with
any device in the network over the same 2-wire pair.
Using multiple transmitters in a HART-compatible network requires assigning a unique address other
than 0 to each transmitter. Assigning an address other than 0 to the transmitter causes the primary mA
output to remain at a constant 4 mA level.
Figure 4-4 shows how to connect wiring for a HART-compatible network.
• The maximum number depends upon the type of transmitters, the method of installation, and
other external factors.
• The primary mA output must produce a 4–20 mA current for the Bell 202 physical layer. The
Bell 202 layer will work when the primary mA output is at or above 2 mA output.
• SMART FAMILY devices require a minimum loop resistance of 250 ohms. Loop resistance
must not exceed 600 ohms.
Connect the mA outputs from each transmitter together so they terminate at a common load resistor,
with at least 250 ohms impedance, installed in series.
Figure 4-4 Typical HART network wiring
Note: For optimum HART communication, make
sure the output loop is single-point-grounded to
an instrument grade ground.
HART comm
tool
RFT9739
field-mount
RFT9739
rack-mount
SMART
FAMILY
device
SMART
FAMILY
device
DC source required for
other HART 4–20mA
passive transmitters 250 ohm
load
PV+
17
PV
−
18
PV+
CN2
−
Z30
PV
−
CN2
−
D30
4–20 mA
IFT9701 IFT9701
4–20 mA
24
DC