Loop Diagnostics Application - Emerson AMS Trex Device Communicator User Manual

User Guide
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4.1
User Guide
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Loop Diagnostics application

The Loop Diagnostics application helps you troubleshoot the wiring of a 4-20 mA current
loop by measuring the voltage and the current. The application can also power a
transmitter or positioner to isolate the device from its current loop and to verify its
operation.
Note
The Trex unit needs the Device Communicator Plus communication module to use the
Loop Diagnostics application. You may also need a second lead set.
If you connect the Trex unit's HART terminals in series with an externally-powered loop,
you can enable Trex Unit Current and have the Trex unit control current (similar to how a
transmitter controls current). Controlling current lets you do the following:
• Verify the input module on a digital control system.
• Verify the cabling between the connection point and the input module on a digital
control system.
• Move a positioner.
If the Trex unit is not connected to an externally-powered loop, you can enable Trex Unit
Power to power one transmitter or positioner. This helps you isolate a problematic device
from its current loop and verify its operation. Powering a device lets you do the following:
• Verify a transmitter in isolation by powering the device and measuring the output.
• Verify a positioner in isolation by powering and moving the positioner.
• Perform wiring continuity checks on cables where no power exists.
WARNING
The Loop Diagnostics application is a generic tool that, if misused, can interfere with an
operating HART loop or may damage the ammeter in the Device Communicator Plus
communication module. Do not provide Trex power or current on a loop that is in
operation. Do not provide external power directly across the Trex mA terminals because
this may damage the ammeter.
Open or close the Loop Diagnostics application
Procedure
1. To open the Loop Diagnostics application, tap the Loop Diagnostics icon on the
Trex Home screen.
2. To close the Loop Diagnostics application, tap Exit.
If you enabled the Trex unit to power a device, the Trex unit stops providing power
when you close the Loop Diagnostics. If the Trex unit was powering a positioner, the
application prompts you to select a current value for the positioner before the
application closes. This allows you to move the positioner to a safe position. After
the selected current value is reached, the Trex unit stops providing power.
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Loop Diagnostics application
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