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APPENDIX D
Troubleshooting Communication Problems
This section contains troubleshooting steps you can take if you are
experiencing communications problems between a field device and your
HART Communicator.
Problem Possible Cause Possible Solution
Intermittent
communication
Insufficient loop resistance
at the HART frequencies.
Add an additional 250 ohm
resistor in series in the loop.
Place the HART Communicator
leads across the resistor and
verify if communication has
been restored.
Noise on the field loop Verify field wiring shield is
grounded at one end only.
Normally,the shieldis grounded
at the control system and
floating atthe field device. See
diagram following this table.
Noise or signal distortion
from the control system
(i.e., noise from power
supply powering field
devices or front end analog
circuitry inside of control
system may be distorting
the HART signal).
Remove field wiring and power
loop with external power supply
and a 250 resistor in the loop.
Verify if communication is
restored with this configuration.
If yes, an oscilloscope may be
used to inspect possible noise
or signal distortion from the
control system. Noise of interest
wouldbeinthe800Hzto
10 KHz range withan amplitude
of 0.5Vpp or larger. Larger
amplitudes below 800 Hz or
above10KHzmayalsoaffect
communication.
Placea0.1microfarad(µf) to a
0.22 µf (Capacitor parameters:
working voltage: 50VDC andno
polarity) across the control
system terminals. Verify if
communication is restored. If
not, place a 250 ohm resistor in
series and verify if
communication is restored. See
diagram following this table.