Troubleshooting - Geokon 4200 Series Instruction Manual

7.

TROUBLESHOOTING

Maintenance and troubleshooting of embedment strain gauges is confined to
periodic checks of cable connections and maintenance of terminals. Once
installed, the gauges 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. Gauges should not be disassembled
in the field.
For additional troubleshooting and support, contact
SYMPTOM: THERMISTOR RESISTANCE IS TOO HIGH

There may be an open circuit. Check all connections, terminals, and plugs. If
a cut is located in the cable, splice according to instructions in Section 4.5.
SYMPTOM: THERMISTOR RESISTANCE IS TOO LOW

There may be a short. Check all connections, terminals, and plugs. If a short
is located in the cable, splice according to instructions in Section 4.5.

Water may have penetrated the interior of the transducer. There is no
remedial action.
SYMPTOM: STRAIN GAUGE 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 strain reading outside the specified compressive or tensile range of
the instrument? The gauge may have become too slack or too tight; inspect
the data to determine whether this is a possibility.

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.

Does the readout or datalogger work with another gauge? If not, it may
have a low battery or possibly be malfunctioning.
SYMPTOM: STRAIN GAUGE FAILS TO READ

Is the cable cut or crushed? Check the resistance of the cable by
connecting an ohmmeter to the sensor leads. Table 7 on page 20 shows
the expected resistance for the various wire combinations. Table 8 on page
20 is provided for you to fill in the actual resistance found. Cable resistance
is approximately 14.7Ω per 1000 ft. (48.5Ω per km) of 22 AWG wire.
Multiply this factor by two to account for both directions.

If the resistance is very high or infinite, the cable is probably broken or cut. If
the resistance is very low, the gauge conductors may be shorted. If a cut or
a short is located in the cable, splice according to the instructions in Section
4.5.

Does the readout or datalogger work with another gauge? If not, it may
have a low battery or possibly be malfunctioning.
MODEL 4200 SERIES STRAIN GAUGES | TROUBLESHOOTING | 19
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GEOKON