16
| TROUBLESHOOTING | GEOKON
6.
TROUBLESHOOTING
Maintenance and troubleshooting is confined to periodic checks of cable
connections and maintenance of terminals. Once installed, these instruments
are usually inaccessible and remedial action is limited. Should difficulties arise,
consult the following list of problems and possible solutions. Return any faulty
gauges to the factory.
Instruments should not be opened in the field.
For
additional troubleshooting and support, contact
GEOKON
.
SYMPTOM: THERMISTOR RESISTANCE IS TOO HIGH
□
Check for an open circuit. Check all connections, terminals, and plugs. If a
cut is located in the cable, splice according to instructions in Section 3.1.
SYMPTOM: THERMISTOR RESISTANCE IS TOO LOW
□
Check for a short circuit. Check all connections, terminals, and plugs. If a
short is located in the cable, splice according to instructions in Section 3.1.
□
Water may have penetrated the interior of the instrument. There is no
remedial action.
SYMPTOM: INSTRUMENT READINGS ARE UNSTABLE
□
Is the readout box position set correctly? If using a datalogger to record
readings automatically, are the swept frequency excitation settings correct?
□
Is the instrument shaft positioned outside the specified range (either
extension or retraction) of the instrument? When the shaft is fully retracted
with the alignment pin inside the alignment slot, the readings will likely be
unstable because the vibrating wire is under-tensioned.
□
Is there a source of electrical noise nearby? Likely candidates are
generators, motors, arc welding equipment, high voltage lines, etc. If
possible, move the instrument cable away from power lines and electrical
equipment or install electronic filtering.
□
Make sure the shield drain wire is connected to ground. Connect the shield
drain wire to the readout using the blue clip.
□
Does the readout or datalogger work with another instrument? If not, it may
have a low battery or possibly be malfunctioning.
SYMPTOM: INSTRUMENT FAILS TO READ
□
Does the readout or datalogger work with another instrument? If not, it may
have a low battery or possibly be malfunctioning.
□
Is the cable cut or crushed? Check the resistance of the cable by connecting
an ohmmeter to the sensor leads; resistance is approximately 48.5 per km
(14.7 per 1000') of 22 AWG wire.
If the resistance is very high or infinite, the cable is probably broken. If the
resistance is very low, the conductors may be shorted. If a break or a short
is present, splice according to the instructions in Section 3.1.
Refer to the expected resistance for the various wire combinations below.
Any other wire combination will result in a measurement of infinite
resistance.
Vibrating Wire Sensor Lead Resistance Levels
Red/Black
Green/White
180
Ω
(
128
Ω
for Model 4420HT)
3000 at 25 °C