Emerson 475 - Page 81

Troubleshooting
81
Table 5-1. Troubleshooting table for the HART protocol
Symptom Possible causes Solution
Intermittent
communication
Insufficient loop current
and voltage at the
device terminals.
Verify there is at least 4
mA and 12V DC at the
device terminals; see
“DC voltage
measurement (HART
terminals)” on page 57.
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. Check wiring
terminations and
exposed signal wire for
damage.
No communication
with device.
Insufficient loop
resistance at the HART
frequencies.
Add an additional 250
ohm resistor in series in
the loop. Place the
leads across the resistor
and verify if
communication has
been restored.
Insufficient loop current
and voltage at the
device terminals.
Verify that there is at
least 4 mA and 12V DC
at the device terminals;
“DC voltage
measurement (HART
terminals)” on page 57.
Device may be set to a
HART address other
than zero (multidrop
mode).
Change Polling mode to
Poll by Address. See
“Changing the HART
polling options” on
page 53.
Cannot connect to a
HART device.
The polling address or
tag may not match the
device.
Check the Polling
Options to ensure the
proper polling type is
selected.
Control system is
communicating
HART, but the Field
Communicator is
not communicating
properly.
HART communication is
being prevented by the
control system.
Stop HART
communications on the
control system and
verify if communication
between the devices
and the 475 is restored.
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