Emerson Rosemount 375, User Manual

Page: 90 / 140

Troubleshooting 5-4
Table 5-1. Troubleshooting table for the HART protocol
Symptom Possible Causes Solution
Intermittent communication Insufficient loop
current and voltage at
the field device
terminals.
Verify there is at least 4 mA and 12V DC at
the field device terminals; see “DC Voltage
Measurement (HART Terminals)” on
page 3-22.
Noise on the field loop.
Noise or signal
distortion from the
control system (i.e.,
noise from the power
supply powering the
field 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
field 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 field device
terminals. Verify there is at least 4 mA and 12V DC at
the field device terminals; “DC Voltage
Measurement (HART Terminals)” on
page 3-22.
Field device may be
set to a HART address
other than zero
(multidrop mode). Change the polling mode to Poll by
Address.
Control system is
communicating HART, but
the 375 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 field devices and the communicator is
restored.
A HART device appears at
multiple addresses. The incorrect polling
addresses may be
used. Change the addresses being polled. See
“Changing the HART Polling Option” on
page 3-17.