Troubleshoot Fieldbus Communication - Emerson AMS Trex User Manual

Troubleshooting
If an oscilloscope is available, use it to look for noise on the loop. Use a scope with
differential mode capability or a battery powered/isolated scope to avoid grounding one
side of the loop. Noise with a frequency of 500 Hz to 10,000 Hz is of particular interest, as
this represents frequencies near the HART frequencies of 1200 and 2200 Hz.
A.2

Troubleshoot fieldbus communication

Symptom
No communication with the
device.
Unable to change the address
of a device.
The Trex unit does not remain
the LAS on a fieldbus segment.
182
Possible causes
The Trex unit is connected to a
fieldbus segment with a host
system and the device on the
same segment is being
commissioned using the host
system.
An internal fuse may be blown.
The Trex unit is unable to
change the address of a device
that is currently the LAS.
A host takes over as the LAS.
Solution
The Trex unit is unable to
communicate with this device
until you go offline and then
back online.
Connect a meter capable of
measuring M ohms to the FF
terminals. An OPEN reading
may indicate a blown fuse.
Establish communication by
putting the Trex unit on the
fieldbus segment first and then
adding one or more devices.
By putting the Trex unit on
first, it remains the LAS and
allows the address change.
When a host is established on a
fieldbus segment, it will take
over as the LAS. No action is
required.
User Guide