Changing A Transmitter Address; Establishing Multi Drop Communication - Emerson Rosemount 644 Reference Manual

Reference Manual
00809-0200-4728, Rev RA
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 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 644 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
A
H
A. Power supply
B. Power supply impedance
C. 250 Ω
D. Hand held terminal
Note
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 to 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.
Configuration
D
B C
F
G
E
E. Computer or DCS
F. HART Interface
G. 4-20 mA
H. 644 HART transmitter
Section 2: Configuration
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