Emerson IFT9701 instruction manual Milliamp output connected to Bell 202 multidrop network

Power Supply and Output Wiring continued

4.4.2Milliamp 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

Before You Begin

Getting Started

HART comm

tool

250ohm load

RFT9739

field-mount

PV+	PV−
17	18

RFT9739

rack-mount

PV+	PV−
CN2−	CN2−
Z30	D30

SMART	SMART
FAMILY	FAMILY
device	device

DC source required for other HART 4–20mA passive transmitters

24

DC

Mounting the Remote Transmitter

4–20 mA

IFT9701

Note: For optimum HART communication, make

4–20 mA sure the output loop is single-point-grounded to an instrument grade ground.

IFT9701

Power Supply and Output Wiring

Model IFT9701 Transmitter Instruction Manual 23