1Loop Test; Multidrop Communication - Emerson Rosemount Reference Manual

Section 3: HART commissioning
April 2014
3.11.1 Loop test
HART 5 Fast Keys
HART 7 Fast Keys
Field Communicator
The Loop Test command verifies the output of the transmitter, the integrity of the loop, and the
operations of any recorders or similar devices installed in the loop.
3.12

Multidrop communication

Multidropping 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
multidropped. With the HART communications protocol, up to 15 transmitters can be
connected on a single twisted pair of wires, or over leased phone lines.
Multidrop installation requires consideration of the update rate necessary from each
transmitter, the combination of transmitter models, and the length of the transmission line.
Communication with transmitters can be accomplished with Bell 202 modems and a host
implementing HART protocol. Each transmitter is identified by a unique address (1–15) 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 3-9. Typical Multidropped Network
Figure 3-9
installation diagram. Emerson Process Management product support can help with specific
requirements for multidrop applications. Note that multidrop is not suitable for safety-certified
applications and installations.
98
3, 5, 1
3, 5, 1
D
E
C
B
A
A. 3144P HART transmitter
B. 4–20 mA
C. Power supply
D. Power supply impedance
shows an example of a typical multidrop network. Do not use this figure as an
F
G
H
E. 250 
F. Handheld terminal
G. Computer or DCS
H. HART interface
Reference Manual
00809-0100-4021, Rev GC
HART® commissioning