Emerson AMS Trex Device Communicator User Manual page 83

User Guide
3.11.1
User Guide
1.800.561.8187
Enable or disable the internal resistors
If the Trex unit is powers the transmitter, there is no prompt/option to enable or disable
the internal 167 Ohm resistor. The Trex unit automatically applies the resistor when you
enable power to a transmitter from the device connection wizard.
If the Trex unit is connected to an externally-powered HART transmitter, the device
connection wizard prompts you if you want to increase loop resistance. The Trex unit then
selects the 250 Ohm or 500 Ohm resistor; you cannot select a specific value. The selected
resistor value is not displayed on the screen.
Procedure
1. If you want the Trex unit to power a 2-wire HART transmitter, do the following:
a) Connect the lead set to the HART + pwr terminals on the Trex unit and to the
communication terminals on the device.
Figure 3-27: Connection for providing power to a 2-wire HART
transmitter
b) In the Field Communicator application, tap HART.
c) Tap Yes when asked if you intend to provide power.
d) Tap Transmitter. The Trex unit applies the internal resistor.
e) Follow any additional prompts to connect to the device.
2. If the Trex unit is connected to an externally-powered 2-wire HART transmitter, do
the following:
a) Connect the lead set to the HART terminals on the Trex unit and to the
communication terminals on the device in-series. (If you are connecting to a
4-wire transmitter, connect the Trex unit in parallel.)
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September 2021
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