Power And Connect To A Hart Device - Emerson AMS Trex User Manual

Field Communicator application
3.
3.12

Power and connect to a HART device

The Trex unit can provide up to 16 volts (at 22.5 mA) to power a HART device. The Trex
unit must have the Device Communicator Plus communication module to power a HART
device (transmitter or positioner).
You do not need to add an external resistor. The Trex unit has a 167 Ohm internal resistor
in the HART + pwr terminals that is used when the Trex unit powers the transmitter.
If you try to apply power from the Trex unit when the device is externally-powered, the
Field Communicator application prevents the Trex unit from supplying power. This
protects the Trex unit from damage.
78
Figure 3-28: Connection for an externally-powered 2-wire transmitter
A. Voltage source
b. Tap HART.
c. Tap No when asked if you intend to provide power.
d. Tap Transmitter.
e. Tap No when asked if you want to change polling. (This assumes the device is at
address zero.)
f. Tap Yes when asked if you want to increase loop resistance.
g. Tap Next.
A message is displayed to indicate the internal resistor is being enabled.
To disable the internal resistor, disconnect the device from the Trex unit, or close
the Field Communicator application.
User Guide