Symptom Possible cause Solution
HART communication is being
prevented by the control
system.
Stop HART communications on
the control system and verify if
communication between the
devices and the Trex unit is
restored.
More than one Trex unit or
other secondary master may be
attached to the control loop.
Ensure there is only one
primary master and one
secondary master on the
control loop.
A HART device appears at the
multiple addresses.
The incorrect polling addresses
may be used.
Change the addresses being
polled.
HART Universal Revision 5 (or
earlier), 6, and 7 devices are on
the same loop.
Put HART Universal Revision 5
or earlier devices on a separate
loop from HART Universal
Revision 6 or 7 devices.
When the Trex unit tries to
power a device, a message
stating voltage still detected at
HART terminals appears.
This message can appear if the
Trex unit connects to a device
that was recently powered.
Some devices may hold voltage
for several minutes after the
power is removed.
The Trex unit asks if you want
to ignore the voltage warning
and proceed with sourcing
power. If you select Yes, Trex
powers the device. You can also
wait a few minutes before
connecting to and powering
the device.
The Trex unit needs to supply
more current than the typical 4
mA to power a positioner. This
can occur when the positioner
needs more current to power
the CPU at faster speed for
diagnostics.
Use the device connection
wizard in the Field
Communicator application to
increase mA.
1. In the Field Communicator
application, connect to
the positioner.
2. Change its polling address
to a non-zero value.
3. Disconnect the positioner,
and restart the Field
Communicator
application.
4. Tap HART.
5. Tap Yes when prompted if
you want to provide
power from the Trex unit.
6. Tap Positioner.
7. Tap Yes when prompted
to increase current.
8. Select the current value.
A.1.1 HART loops
Verify the HART loop current and voltage on the device. Almost all devices need at least 4
mA and 12V DC to operate properly. If there are multiple devices on a multidrop loop, set
Troubleshooting
User Guide
September 2021
180 User Guide
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