Reference Manual
00809-0200-4841, Rev BA
December 2014
Section 3: Installation
18
3.4.3
Wiring to allow HART communication
If HART communications is required, a 250 Ohm (minimum), 0.25 W load resistor must be
installed in the loop. (See
“Load limitations” on page 114
).
Note
When the transmitter is used with a Rosemount 3490 Series Control Unit, there is no
need to install an external load resistor in the loop because a suitable resistor is built in
to the control unit.
If the transmitter is being supplied through a safety barrier, ensure the type chosen will pass
HART information.
After the load resistor is installed, a Field Communicator can be connected across the load
resistor, or across the loop at any point downstream of the load resistor.
It is the responsibility
of the installer to ensure that any Field Communicator used in the hazardous area is
suitably certified
.
Note
Make sure that the instruments in the loop are installed according to intrinsically-safe
field wiring practices and control drawings, when applicable.
3.4.4
Lightning / surge protection and other loop devices
If the area is prone to lightning strikes or voltage surges, a suppressor device may be installed
between the transmitter and the control unit.
If an additional loop-powered device or separately powered device is included in the two-wire
loop, ensure the transmitter receives a minimum voltage of 12 Vdc (see
).
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