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Reference Manual
00809-0200-4728, Rev SA
Configuration
July 2018
Configuration
2.12
Establishing multi drop communication
Multi dropping
refers to the connection of several transmitters to a single communications transmission
line. Communication between the host and the transmitters takes place digitally with the analog output
of the transmitters deactivated.
Many Rosemount transmitters can be multi dropped. With the HART Communications protocol, up to
15 transmitters can be connected on a single twisted pair of wires or over leased phone lines.
A Field Communicator can test, configure, and format a multidropped Rosemount 644 Transmitter in
the same way as in a standard point-to-point installation. The application of a multidrop installation
requires consideration of the update rate necessary from each transmitter, the combination of
transmitter models, and the length of the transmission line. Each transmitter is identified by a unique
address (1–15) and responds to the commands defined in the HART protocol. A HART-based
Communicator can test, configure, and format a multi dropped transmitter the same as in a standard
point-to-point installation.
Note
Multi drop is not suitable for safety-certified applications and installations.
Figure 2-23. Typical Multi Dropped Network
Note
Rosemount 644 Transmitters are set to address 0 at the factory, allowing them to operate in the
standard point-to-point manner with a 4–20 mA output signal. To activate multi drop communication,
the transmitter address must be changed to a number between 1 and 15. This change deactivates the
4–20 mA analog output, sending it to 4 mA. The failure mode current also is disabled.
2.12.1
Changing a transmitter address
To activate multi drop communication, the transmitter poll address must be assigned a number from
1–15 for HART Revision 5, and 1–63 for HART Revision 7. Each transmitter in a multi dropped loop must
have a unique poll address.
A. Power supply
B. Power supply impedance
C. 250
Ω
D. Hand held terminal
E. Computer or DCS
F. HART Interface
G. 4–20 mA
H. Rosemount 644 HART Transmitter
A
B C
D
E
F
G
H
Summary of Contents for Rosemount 644 with HART Protocol
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