Ams trex™ Device Communicator

4.8
Power a positioner
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.
User Guide 
Loop Diagnostics application
September 2021
User Guide 
141

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 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.
Procedure
1. Connect the lead set to the 
HART + pwr
terminals on the Trex unit and to the
positioner.
Figure 4-16: Connection for powering a positioner
2. On the Loop Diagnostics screen, tap 
Trex Unit Power
.
3. Select one of the following:
Option
Description
Power Positioner with 4 mA (0%)
Power a positioner using 4 mA.
Power Positioner with 20 mA (100%)
Power a positioner using 20 mA.
Power Positioner with other mA value
Power a positioner using a specified mA
value.
4. Tap 
OK
.
Loop Diagnostics
is now powering the positioner and measuring voltage and
current. The 
Trex Unit Current
option is also enabled.
5. To change the current value, tap one of the quick current buttons (4 mA, 8 mA, 12
mA, 16 mA, 20 mA), or use the up and down arrow keys to manually increase the
current value. The default increment is 0.1 mA.
6. To stop powering the device, do one of the following:
Loop Diagnostics application
User Guide
September 2021
142
User Guide

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•
Tap 
Trex Unit Power
to set the option to 
OFF
. You are prompted to select a
power option to set the position of the valve.
•
Tap 
Exit
. You are prompted to select a power option to set the position of the
valve.
•
Remove the lead set from the Trex unit. You are