Emerson 375 User Manual page 88

5-4
Table 5-1. Troubleshooting table for HART protocol
Symptom
Intermittent communication Insufficient loop
No communication with
field device.
Control system is
communicating HART, but
the 375 is not
communicating properly.
Possible Causes
current and voltage at
the field device
terminals.
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
Insufficient loop
resistance at the HART
frequencies.
Insufficient loop
current and voltage at
the field device
terminals.
Field device may be
set to a HART address
other than zero
(multidrop mode).
HART communication
is being prevented by
the control system.
Solution
Verify there is at least 4 mA and 12V DC at
the field device terminals; see "DC Voltage
Measurement (HART Terminals)" on
page 3-21.
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 field device terminals; "DC
Voltage Measurement (HART Terminals)"
on page 3-21.
Change Polling mode to an option other
than "Never Poll", e.g., Digital Poll.
Stop HART communications on the control
system and verify if communication between
the field devices and the communicator is
restored.
Troubleshooting