Ams trex™ Device Communicator

Figure 4-10: Read current for an analog output loop check
The Trex unit is connected to an analog output and is measuring current from the mA
terminals. You can connect the Trex unit at various points on the current loop, including a
junction box, device connection point, etc.
 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.
A. Analog output
Figure 4-11: Connect to an externally-powered positioner and read current
A. Analog output
User Guide 
Loop Diagnostics application
September 2021
User Guide 
137

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Figure 4-12: Measure current from an externally-powered transmitter device with
test terminals
The Trex unit measures current from the mA terminals on an externally-powered loop
without breaking the loop and connecting the ammeter (mA terminals) in-series.
 WARNING
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.
Note
Please review your device documentation for additional information about reading current
from the test terminals. The orientation of the terminals on your device may be different.
The drawing below is an example.
A. Voltage source
Loop Diagnostics application
User Guide
September 2021
138
User Guide

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Figure 4-13: Power and control current to simulate a transmitter on an unpowered