Reference Manual
00809-0100-4840, Rev. BA
July 2008
Rosemount 3100 Series
3-14
Remote Temperature
Sensor
The Rosemount 3102 and Rosemount 3105 accept input from a remote
temperature sensor (see “Accessories for The Rosemount 3101/3102/3105“
on page A-9.)
This is a thermistor-based temperature sensor designed for use with The
3102 and The 3105. When connected to the transmitter, the remote
temperature sensor may be installed in a hazardous area without the need for
any additional protection / barriers.
NOTE:
Avoid connecting any other temperature sensor to The 3102 and The 3105.
Full installation instructions are supplied with the temperature sensor, but it
should be mounted out of direct sunlight in a position so that it can give a
representative reading of the air temperature between the liquid surface and
the transmitter.
Wiring to Allow
HART
®
Communication
If HART communications (available on The 3102 and The 3105) is required,
a 250 Ohm, 0.25 W load resistor must be installed in the loop.
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 375 Field Communicator can be
connected across the load resistor, or across the loop at any point
downstream of the load resistor.
NOTE!
Make sure that the instruments in the loop are installed according to
intrinsically-safe field wiring practices and control drawings, when applicable.
Lightning / Surge
Protection and Other
Loop Devices
Loop-powered or separately powered devices can be included in the two-wire
loop if the transmitter receives a minimum voltage of 12 Vdc at 21 mA loop
current.
If the area is prone to lightning strikes or voltage surges, a suppressor device
should be installed between the transmitter and the control unit.
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