Ams trex™ Device Communicator

Figure 4-4: Power a HART transmitter
The Trex unit measures both voltage and current from the HART + pwr terminals. An
internal 167 Ohm resistor is used when the Trex unit powers the device.
 CAUTION
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.
Figure 4-5: Measure voltage on an externally-powered HART transmitter
A. Voltage source
Loop Diagnostics application
User Guide
September 2021
134
User Guide

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Figure 4-6: Power and control current to a positioner
The Trex unit measures both voltage and current from the HART + pwr terminals.
Figure 4-7: Connect to an externally-powered positioner in-parallel
The Trex unit measures voltage from the HART terminals. Voltage measurements can be
taken at various points to identify voltage drops along the loop.
A. Current source
User Guide 
Loop Diagnostics application
September 2021
User Guide 
135

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Figure 4-8: Connect to an externally-powered positioner in-series
The Trex unit controls current from the HART terminals.
A. Voltage source
Figure 4-9: Control current to simulate a transmitter on an externally-powered loop
The Trex unit controls current from the HART terminals, which simulates a transmitter.
The Trex unit controls current the same way as a transmitter controls current. The Trex
unit is connected to the analog input (AI) channel.
You can connect the Trex unit at various points on the current loop, including a junction
box, device connection point, etc.
A. Analog input
Loop Diagnostics application
User Guide
September 2021
136
User Guide

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