Establishing Multidrop Communication - Emerson Rosemount 3051 Reference Manual

Reference Manual
00809-0100-4007
2.13

Establishing multidrop communication

Multidrop communication 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.
To install multidrop communication, you must consider the update rate necessary from
each transmitter, the combination of transmitter models, and the length of the
transmission line. You can communicate with transmitters with HART
host implementing HART protocol. Each transmitter is identified by a unique address and
responds to the commands defined in the HART protocol. Field Communicators and AMS
Device Manager can test, configure, and format a multidropped transmitter the same way
as a transmitter in a standard point-to-point installation.
Figure 2-19
installation diagram.
Note
A multidrop transmitter in HART Revision 7 mode has a fixed analog output of 4 mA for all
but one device. Only one device is allowed to have an active analog signal.
Figure 2-19: Typical Multidrop Network
A. HART modem
B. Power supply
Emerson sets the Rosemount
operation in the standard point-to-point manner with a 4-20 mA output signal. To activate
multidrop communication, you must change the transmitter address to a number from 1
to 15 for HART Revision 5 or 1 to 63 for HART Revision 7. This change deactivates the 4-20
mA analog output, sending it to 4 mA. It also disables the failure mode alarm signal, which
is controlled by the upscale/downscale switch position. HART messages communicate
failure signals in multidropped transmitters.
Reference Manual
shows a typical multidrop network. This figure is not intended as an
A
™
3051 to address zero ( 0 ) at the factory, which allows
B
Configuration
August 2019
®
modems and a
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