Ams trex™ Device Communicator

 CAUTION
Do not connect lead sets to the HART and HART + pwr terminals at the same time.
Procedure
1. Connect the lead set to the HART terminals on the Trex unit and to the externally-
powered device.
2. View the 
Measured Voltage
section on the 
Loop Diagnostics
screen.
4.11.2
Measure the control system output
Measure loop current to ensure a device or distributed control system is sending the
correct value. You can measure loop current from 0 to 25 mA on a 4-20 mA current loop.
Note
Measurements are for reference purposes only. Do not make critical process-control
decisions based on these measurements.
 WARNING
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.
 WARNING
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.
Procedure
1. Connect the lead set to the 
mA
terminals on the Trex unit and to a connection point
on the loop.
The Trex unit can be connected at various point along the loop to measure current.
Loop Diagnostics application
User Guide
September 2021
148
User Guide

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Figure 4-18: Example connection for measuring current
A. Analog output.
2. In the 
Loop Diagnostics
application, view the measured current at the top of the
screen.
4.11.3
Simulate a transmitter on an externally-powered loop
for a loop check
The Loop Diagnostics application can control current to simulate a 2-wire transmitter on
an externally-powered loop. In this setup, the digital control system is powering the
current loop and the Trex unit is controlling the current that is input into the digital control
system.
Procedure
1. Connect the lead set to the HART terminals on the Trex unit and to the powered
4-20 mA current loop.