Emerson 475, User Manual

Page: 73 / 114

Troubleshooting 5-3
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 3-18.
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 3-18.
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 3-15.
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.
More than one Field
Communicator or other
Secondary Master may be
attached to the control loop. Ensure there is only one
Primary Master and one
Secondary Master on the
control loop.
A HART device appears
at multiple addresses. The incorrect polling
addresses may be used. Change the addresses being
polled. See “Changing the
HART Polling Options” on
page 3-15.
HART revision 5 (or earlier), 6,
and 7 devices are on the
same loop Put HART 5 or earlier devices
on a separate loop from
HART 6 or 7 devices.