Emerson AMS Trex, User Manual

Page: 131 / 214

4 Loop Diagnostics application
Topics covered in this chapter:
• Open or close the Loop Diagnostics application
• Loop Diagnostics screen
• Powering transmitters or positioners from Loop Diagnostics
• Voltage and current measurements in Loop Diagnostics
• Wiring diagrams for the Loop Diagnostics application
• Power a 2-wire transmitter
• Power a 2-wire transmitter and measure analog output
• Power a positioner
• Stroke a valve
• Settings for controlling current
• Loop checks
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.
Loop Diagnostics application
User Guide 123