Wiring diagrams for HART devices and the Field Communicator application

The Trex unit can communicate with a device from the control room, on the bench, or any wiring termination point in the loop. Connect the lead set to the Trex unit and to the communication terminals on the device or across the resistor.

Below each diagram, a table lists the expected prompts from the device connection wizard and the answers to complete the connection. The prompts appear only if the Field Communicator application could not automatically detect or connect to the device.

Power and connect to a 2-wire HART transmitter

Note: When the Trex unit powers the HART transmitter, an external resistor is not needed. The Trex unit uses an internal resistor that is automatically used when you enable the Trex unit to power the transmitter.

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 may prevent communications.

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	Yes
Are you providing power to a transmitter or positioner?	Transmitter
Change Polling Option?	Tap Yes if the device is not at address zero.

Connect to a powered WirelessHART device (with its battery attached)

CAUTION:

Do not use the Trex unit to power a WirelessHART device. Providing power to a WirelessHART device may damage the device.

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	No
Leads are attached to:	Transmitter
Change Polling Option?	Tap Yes if the device is not at address zero.

Connect to an externally-powered 2-wire HART transmitter

If the transmitter is at address zero, the Trex unit may automatically detect and connect to the device without any prompts from the device connection wizard.

1. Voltage source

Connect to an externally-powered 2-wire HART transmitter and use the Trex internal resistor

Note: The Trex unit must be connected in series with the transmitter to use the internal resistor.

1. Voltage source

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	No
Leads are attached to:	Transmitter
Change Polling Option?	Tap Yes if the device is not at address zero.
Increase loop resistance?	Tap Yes to enable the internal resistor.

Connect to a 4-wire HART transmitter

If you have a 250 Ohm resistor, you can insert it in between the device terminals and connect the lead set across the resistor. Otherwise, you can enable the internal resistor in the device connection wizard.

Note: Ensure you review the device documentation for connecting/setting up HART communication. Devices may have different terminals or requirements.

1. Voltage source

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	No
Leads are attached to:	Transmitter
Change Polling Option?	Tap Yes if the device is not at address zero.
Increase loop resistance?	Tap Yes if there is no external resistor between the device terminals.

Power and connect to a HART positioner

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	Yes
Are you providing power to a transmitter or positioner?	Positioner
Change Polling Option?	Tap Yes if the device is not at address zero.
Increase loop current?	Tap Yes to increase the current from 4 mA to another value, if the device did not initially communicate.

Connect to an externally-powered HART positioner

1. Current source

Device connection wizard prompts	Answer
Do you intend to provide power from the Trex unit?	No
Leads are attached to:	Positioner
Change Polling Option?	Tap Yes if the device is not at address zero.
Increase loop current?	Tap Yes to increase the current from 4 mA to another value, if the device did not initially communicate.