Appendix A Troubleshooting; Troubleshoot Hart Communication - Emerson AMS Trex User Manual

Appendix A
Troubleshooting
Topics covered in this appendix:
•
•
A.1

Troubleshoot HART communication

Symptom
"No Voltage Detected"
message is displayed.
There is intermittent
communication.
There is no communication
with device.
User Guide
Troubleshoot HART communication
Troubleshoot fieldbus communication
Possible cause
The lead set is improperly
connected to the device.
The Trex unit is connected to a
4-wire device or a wireless
device that is powered by its
battery.
Insufficient loop current and
voltage at the device terminals.
Noise on the loop, or noise or
signal distortion from the
control system. For example,
noise from the power supply
powering the devices, or front
end analog circuitry inside the
control system may be
distorting the HART signal.
Poor wiring.
Insufficient loop resistance at
the HART frequencies.
Insufficient loop current and
voltage at the device terminals.
The AC adapter is attached to
the Trex unit.
Troubleshooting
Solution
Attach the lead set to the
device.
None. This is expected
behavior.
Verify there is at least 4 mA and
12 VDC at the device terminals.
An oscilloscope can help
determine noise or signal
distortion of HART signals.
Check the wiring terminations
and exposed signal wire for
damage.
Add an additional 250 ohm
resistor in series in the loop.
Place the leads across the
resistor and verify
communication occurs.
Verify there is at least 4 mA and
12 VDC at the device terminals.
Remove the AC adapter from
the Trex unit and try to connect
to the device.
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