Ams trex™ Device Communicator

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.
3. To disable the internal resistor, disconnect the device from the Trex unit, or close
the Field Communicator application.
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.
Field Communicator application
User Guide
September 2021
84
User Guide

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 CAUTION
•
The Trex unit cannot power a 4-wire device. Do not connect Trex unit to the power
terminals of a 4-wire device. This can blow a fuse inside the Trex unit. The repair/
replacement will need to be completed at an authorized service center.
•
Remove the USB cable from the Trex unit before connecting to a device.
•
Do not use the Trex unit to power a 
Wireless
HART device. Providing power to a
Wireless
HART device may damage the device.
 WARNING
Do not add any external power to the device when the Trex unit is powering the device.
This can blow a fuse inside the Trex unit. The repair/replacement will need to be
completed at an authorized service center. Ensure the device is disconnected from the
loop/segment and no other wires are connected to the device before providing power
from the Trex unit.
Procedure
1. Connect the lead set to the HART + pwr terminals on the Trex unit and to the
communication terminals on the device.