High-frequency noise Possible cause Action
Variable-frequency drives
installed near the fieldbus
segment may not have the
recommended grounding and
filtering.
Check the grounding and
filtering that are used.
Fieldbus signal Possible cause Action
Lower than expected The Trex unit is attached far
away from the FOUNDATION
fieldbus device that is
transmitting the signal.
Connect the Trex unit directly
to the communication
terminals on the device. No
other wires should be
connected to the device.
Ensure the device is
disconnected from any other
terminators or devices.
Connect the Trex unit to a
connection point that is closer
to the device on the fieldbus
segment.
The cable between the Trex unit
and the device is damaged.
Determine if the signal loss is
acceptable. If it is not, replace
the cable between the Trex unit
and the device.
Fieldbus signals can be received
when they are 250 mVp-p or
higher, so loss of signal
amplitude is tolerable.
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.
User Guide Fieldbus Diagnostics application
September 2021
User Guide 177
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