Emerson AMS Trex Device Communicator User Manual page 16

AMS Trex Device Communicator overview
September 2021
2.5.1
16
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WARNING
• 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.
• Do not connect lead sets to the HART and HART + pwr terminals at the same time. If
the lead sets are connected to devices, this increases the chance of wiring mistakes and
could create a short in the HART loop.
• 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.
• Do not use the Trex unit to power a WirelessHART device. Providing power to a
WirelessHART device may damage the device.
• Do not connect the mA terminals (ammeter) in parallel with a powered 4-20 mA
current loop. Ammeters have low resistance. This can disrupt the loop and cause
devices to report incorrect values or positioners to move unexpectedly.
• Do not connect the mA terminals on the Trex unit to a power supply that is not current
limited to 250 mA. This can blow a fuse inside the Trex unit. The repair/replacement
will need to be completed at an authorized service center.
Ammeter on the Device Communicator Plus
communication module
The Device Communicator Plus communication module has several ammeters for reading
current:
1. Ammeter in the mA terminals. This ammeter is intended for quick measurements
and is for reference only.
2. Ammeter in the HART + pwr terminals. This ammeter is used when the Trex unit is
powering a transmitter. This ammeter is intended for tasks including digital-to-
analog trims where a higher accuracy ammeter is required.
3. Ammeter in the HART + pwr and HART terminals. This ammeter is used when the
Trex unit is controlling current or is powering a positioner. The ammeter is intended
to give feedback on the output current from the Trex unit and is for reference only.
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