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.
- 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.
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
- In the Field Communicator application, tap HART.
- Tap Yes when prompted if you want the Trex unit to power the device.
If you selected Positioner, the Trex unit provides power and 4 mA.
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.