Power a 2-wire transmitter

The Trex unit can provide up to 16 volts (at 22.5 mA) to power a HART device. You do not need to add an external resistor. The Trex unit has a 167 Ohm internal resistor in the HART + pwr terminals that is used when the Trex unit provides power to the transmitter.

If you try to apply power from the Trex unit when the device is externally-powered, the Loop Diagnostics application prevents the Trex unit from supplying power. This protects the Trex unit from damage.

CAUTION:
Remove the USB cable from the Trex unit before connecting to a device.
CAUTION:
Do not add any external power to the device when the Trex unit is powering the device. This can blow a fuse inside the Trex unit. The repair/replacement will need to be completed at an authorized service center. Ensure the device is disconnected from the loop/segment and no other wires are connected to the device before providing power from the Trex unit.
Note: Do not insert a resistor in parallel with either the HART + pwr or HART terminals on the Trex unit, or in parallel with the device's communication terminals. This will interfere with the current measurements and may prevent communication.
  1. Connect the lead set to the HART + pwr terminals on the Trex unit and to the transmitter.

    Power a 2-wire transmitter

  2. On the Loop Diagnostics screen, tap Trex Unit Power.
  3. Tap Power Transmitter.
    The Trex unit uses an internal resistor while powering the device.
  4. Tap OK.
    Loop Diagnostics is now powering the transmitter and measuring voltage and current.
  5. To stop powering the device, do one of the following:
    • Tap Trex Unit Power to set the option to Off.
    • Tap Exit.
    • Remove the lead set from the Trex unit.