Emerson AMS Trex User Manual page 184

Fieldbus Diagnostics application
High-frequency noise
Higher than expected
Fieldbus signal
Lower than expected
176
Possible cause
There may be loose wire
connections.
Water or moisture may be in
the device's terminal housing.
A cable may be damaged.
Variable-frequency drives
installed near the fieldbus
segment may not have the
recommended grounding and
filtering.
Possible cause
The Trex unit is attached far
away from the FOUNDATION
fieldbus device that is
transmitting the signal.
The cable between the Trex unit
and the device is damaged.
Action
Check for loose connections.
Vibration from nearby motors
or wind gusts may cause loose
connections to be displayed as
high-frequency noise.
Check the device's terminal
housing.
Use the signal or DC voltage
measurement to find the cable
portion that may be damaged.
Visually inspect the cables, and
test the resistance between the
two wires and each wire to the
ground.
Check the grounding and
filtering that are used.
Action
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.
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.
User Guide