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.