Ams trex™ Device Communicator

Power/Help section
: Lets you enable/disable the Trex unit to power a transmitter or
positioner. The connection diagram on the right shows the terminals on the Trex unit
where measurements are being read.
By default, the HART and mA terminals are circled in green on the connection diagram.
The diagram shows you one setup for reading voltage on the HART terminals and
current on the mA terminals when 
Trex Unit Power
 is off. (This setup lets you take the
measurements without interrupting the 4-20 mA current loop by connecting the Trex
HART terminals to a transmitter's communication terminals and connecting the Trex mA
terminals to a transmitter's test terminals.) The connection diagram is updated based on
the options you select (
Trex Unit Power
 and 
Trex Unit Current
).
User Guide 
Loop Diagnostics application
September 2021
User Guide 
127

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C.
Current control/output section
: Lets you use multiple options for controlling current
including quick buttons, keypad, and up/down keys for immediately adjusting current or
for gradually changing current over 1 to 5 seconds. These options are displayed when
either the 
Trex Unit Power
 or 
Trex Unit Current
 is 
ON
.
Loop Diagnostics application
User Guide
September 2021
128
User Guide

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Figure 4-2: Loop Diagnostics when powering a positioner and taking measurements
A. The voltage measured at the HART or HART + pwr terminals
B. Enable/disable the Trex unit to provide power to a transmitter or power and source
current to a positioner. This lets you isolate a problematic device from its HART loop and
verify its operation. Use the HART + pwr terminals on the Trex unit.
C. Enable/disable the Trex unit to control current to an externally-powered positioner or to
an analog input card on a digital control system. The Trex unit controls current the same
way as a transmitter. Use the HART terminals on the Trex unit when the 
Trex Unit Power
option is off. This option is automatically enabled if 
Trex Unit Power
 is on and the Trex
unit is powering a positioner.
D. Change the settings for supplying/controlling current, including the values of the quick
buttons, the scale for the up and down arrows, and the time to change to a new current
value. This option is enabled only when 
Trex Unit Power
 or 
Trex Unit Current
 is on.
E. The quick buttons to control the current to the positioner or 4-20 mA current loop. You
can change the values of the buttons from the 
More Options
 button.
User Guide 
Loop Diagnostics application
September 2021
User Guide 
129

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F. The current measured at the mA, HART + pwr, or HART terminals on the Trex unit. If 
Trex
Unit Power
 is off and 
Trex Unit Current
 is on, use the HART terminals to measure
current.
G. The terminals that are controlling/measuring current and voltage are circled in green.
Tap the image to see a larger version.
H. The current that the Trex unit is supplying.
I. The up and down arrows to gradually increase or decrease the current. The default
increment is 0.10 mA. You can change this increment from 
More Options
.
J. Tap the pencil icon to enter a new current value to be supplied.
4.2.1
View the connection diagram as a full-screen image
The 
Loop Diagnostics
screen displays an image of the terminals on the Trex unit to help
you make the correct connection and to see where the measurements are read. The image
changes to display the correct connection for a desired task, based on the measurements
or options you selected. You can view a full-screen version of this image.