Emerson 475 User Manual page 73

Troubleshooting
Table 5-1. Troubleshooting Table for the HART Protocol
Symptom
Intermittent
communication
No communication with
device.
Cannot connect to a
HART device
Control system is
communicating HART,
but the Field
Communicator is not
communicating properly.
A HART device appears
at multiple addresses.
Possible Causes
Insufficient loop current 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.
Insufficient loop 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).
The polling address or tag
may not match the device.
HART communication is being
prevented by the control
system.
More than one Field
Communicator or other
Secondary Master may be
attached to the control loop.
The incorrect polling
addresses may be used.
HART revision 5 (or earlier), 6,
and 7 devices are on the
same loop
Solution
Verify there is at least 4 mA
and 12V DC at the device
terminals; see "DC Voltage
Measurement (HART
Terminals)" on page 3-18.
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 3-18.
Change Polling mode to Poll
by Address. See "Changing
the HART Polling Options" on
page 3-15.
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.
Ensure there is only one
Primary Master and one
Secondary Master on the
control loop.
Change the addresses being
polled. See "Changing the
HART Polling Options" on
page 3-15.
Put HART 5 or earlier devices
on a separate loop from
HART 6 or 7 devices.
5-3