D-1

APPENDIX DTroubleshooting Communication Problems

Thissection contains troubleshooting steps you can take ifyou are

experiencingcommunicati onsproblems between a field device and your

HARTCommunicator.

Problem PossibleCause PossibleSolution

Intermittent
communication Insufficient loop resistance
atthe HART frequenci es. Addan additio nal 250 ohm
resistorin series in the loop.
Placethe HART Communicator
leadsacross the resistorand
verifyif communica tion has
beenrestored.
Noiseon the field loop Verifyfield wiring shield is
groundedat one end on ly.
Normally,the shield is grounded
atthe control sys tem and
floatingat the field device.See
diagramfollo wing this table.
Noiseor signal distortion
fromthe control syst em
(i.e.,noise fr om power
supplypowerin g field
devicesor front end analog
circuitryinside of control
systemmay be dist orting
theHART signal).
Removefield wiring and power
loopwith exter nal power supply
anda 250 resistor in the loop.
Verifyif communication is
restoredwith this configuration.
Ifyes, an oscilloscope m ay be
usedto inspect possiblenoise
orsignal distortion from the
controlsystem. Noise of interest
wouldbeinthe800Hzto
10KHz range with an amplitude
of0.5Vpp or l arger.Large r
amplitudesb elow 800 Hz or
above10KHzmayalsoaffect
communication.
Placea0.1microfarad(µf)toa
0.22 µf(Capacitorparameters:
workingvoltage: 50V DC and no
polarity)across t he control
systemterminals. Verify if
communicationi s restored. If
not,place a 250 ohm resist or in
seriesand verify if
communicationi s restored. See
diagramfollo wing this table.