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.
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.