Ams trex™ Device Communicator

loop
Note
The Trex unit is connected to a 4-wire terminal block. Consult the host documentation for
more information.
A. Analog input
4.6
Power a 2-wire transmitter
The Trex unit can provide up to 16 volts (at 22.5 mA) to power a HART device when using a
Trex unit with a Device Communicator Plus communication module. 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 provides power to the transmitter.
If you try to apply power from the Trex unit when the device is externally-powered, the
Loop Diagnostics application prevents the Trex unit from supplying power. This protects
the Trex unit from damage.
 CAUTION
Remove the USB cable from the Trex unit before connecting to a device.
 CAUTION
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.
Note
Do not insert a resistor in parallel with either the HART + pwr or HART terminals on the
Trex unit, or in parallel with the device's communication terminals. This will interfere with
the current measurements and may prevent communication.
User Guide 
Loop Diagnostics application
September 2021
User Guide 
139

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Procedure
1. Connect the lead set to the 
HART + pwr
terminals on the Trex unit and to the
transmitter.
Figure 4-14: Power a 2-wire transmitter
2. On the 
Loop Diagnostics
screen, tap 
Trex Unit Power
.
3. Tap 
Power Transmitter
.
The Trex unit uses an internal resistor while powering the device.
4. Tap 
OK
.
Loop Diagnostics
is now powering the transmitter and measuring voltage and
current.
5. To stop powering the device, do one of the following:
•
Tap 
Trex Unit Power
to set the option to 
Off
.
•
Tap 
Exit
.
•
Remove the lead set from the Trex unit.