Multidrop Communication - Emerson Rosemount 248 Reference Manual

Configuration
May 2019
3.5

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.
A Field Communicator can test, configure, and format a multidropped Rosemount 248
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.
Figure 3-3: Typical Multidropped Network
A. Rosemount 248 HART transmitter
B. Power supply
Figure 3-3
diagram. Contact Emerson product support with specific requirements for multidrop
applications.
Note
Rosemount 248 Transmitters are set to address 0 at the factory, which allows them to
operate in the standard point-to-point manner with a 4–20 mA output signal. To activate
multidrop communication, the transmitter address must be changed to a number
between 1 and 15. This change deactivates the 4–20 mA analog output and sets it to 4 mA
and disables the current failure mode.
42
A
shows a typical multidrop network. Do not use this figure as an installation
B
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