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.