Power and connect to a HART device

The Trex unit can provide up to 16 volts (at 22.5 mA) to power a HART device. The Trex unit must have the Device Communicator Plus communication module to power a HART device (transmitter or positioner).

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 powers the transmitter.

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

CAUTION:
  • The Trex unit cannot power a 4-wire device. Do not connect Trex unit to the power terminals of a 4-wire device. This can blow a fuse inside the Trex unit. The repair/replacement will need to be completed at an authorized service center.
  • Remove the USB cable from the Trex unit before connecting to a device.
  • Do not use the Trex unit to power a WirelessHART device. Providing power to a WirelessHART device may damage the device.
Warning: 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.
  1. Connect the lead set to the HART + pwr terminals on the Trex unit and to the communication terminals on the device.

    Power a HART transmitter

    Power a HART positioner

  2. In the Field Communicator application, tap HART.
  3. Tap Yes when prompted if you want the Trex unit to power the device.
  4. Tap Transmitter or Positioner.
    If you selected Positioner, the Trex unit provides power and 4 mA.
  5. Follow any additional prompts.
    You may see additional prompts if the Trex unit cannot connect to the device. For example, you may be prompted to review the polling address. For a positioner, you may be asked to increase current (mA) to increase the value from the original 4 mA. The Online menu or the device dashboard displays, depending on the device type.