Emerson AMS Trex User Manual page 185

Fieldbus signal
Higher than expected
User Guide
Possible cause
There are too many terminators
on the fieldbus segment.
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.
The Trex unit is powering a
FOUNDATION fieldbus device,
but it is not attached directly to
the device 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.
The fieldbus segment is missing
a terminator.
Fieldbus Diagnostics application
Action
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.
To see the normal fieldbus
signal amplitudes, connect the
Trex unit to the trunk of the
connector block.
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.
None. This is normal when the
Trex unit is providing power.
The higher signal level is
acceptable on these
terminators.
Attach another fieldbus
terminator to the fieldbus
segment.
177