Emerson 475 User Manual page 81

Troubleshooting
Table 5-1. Troubleshooting table for the HART protocol
Symptom Possible causes
Intermittent Insufficient loop current
communication and voltage at the
device terminals.
Noise on the field loop.
Noise or signal distortion
from the control system,
i.e., noise from the
power supply powering
the devices or front end
analog circuitry inside
the control system may
be distorting the HART
signal.
Poor wiring.
No communication Insufficient loop
with device. resistance at the HART
frequencies.
Insufficient loop current
and voltage at the
device terminals.
Device may be set to a
HART address other
than zero (multidrop
mode).
Cannot connect to a The polling address or
HART device. tag may not match the
device.
Control system is HART communication is
communicating being prevented by the
HART, but the Field control system.
Communicator is
not communicating
properly.
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Solution
Verify there is at least 4
mA and 12V DC at the
device terminals; see
"DC voltage
measurement (HART
terminals)" on page 57.
Check wiring
terminations and
exposed signal wire for
damage.
Add an additional 250
ohm resistor in series in
the loop. Place the
leads across the resistor
and verify if
communication has
been restored.
Verify that there is at
least 4 mA and 12V DC
at the device terminals;
"DC voltage
measurement (HART
terminals)" on page 57.
Change Polling mode to
Poll by Address. See
"Changing the HART
polling options" on
page 53.
Check the Polling
Options to ensure the
proper polling type is
selected.
Stop HART
communications on the
control system and
verify if communication
between the devices
and the 475 is restored.