Fieldbus signal Possible cause Action
There are too many terminators
on the fieldbus segment.
Review the number of
terminators. A fieldbus
segment should have two
terminators.
Note
The Trex unit adds two
terminators when it powers a
FOUNDATION fieldbus device.
Higher than expected The Trex unit is attached to a
block with short-circuit
protection.
Non-standard terminators are
used to achieve short-circuit
protection. This slightly changes
the fieldbus signal, and the
signal amplitude is increased by
20 to 30 percent.
To see the normal fieldbus
signal amplitudes, connect the
Trex unit to the trunk of the
connector block.
The Trex unit is powering a
FOUNDATION fieldbus device,
but it is not attached directly to
the device terminals.
Ensure the Trex unit is
connected directly to a single
FOUNDATION fieldbus device.
No other wires should be
connected to the device.
Ensure there are no resistors in-
series with the device's
terminals.
When the Trex unit powers a
FOUNDATION fieldbus device,
non-standard terminators are
used to meet Intrinsic Safety
requirements. This slightly
changes the fieldbus signal, and
the signal amplitude is increased
by 20 to 30 percent. The signal
amplitude for the Trex unit is not
impacted.
None. This is normal when the
Trex unit is providing power.
The higher signal level is
acceptable on these
terminators.
The fieldbus segment is missing
a terminator.
Attach another fieldbus
terminator to the fieldbus
segment.
Fieldbus Diagnostics application
User Guide 177
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