Troubleshooting - Geokon 4200 Series Instruction Manual

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7. TROUBLESHOOTING

Maintenance and troubleshooting of embedment strain gages is confined to periodic checks of
cable connections and maintenance of terminals. Once installed, the gages are usually
inaccessible and remedial action is limited. Should difficulties arise, consult the following list of
problems and possible solutions. Return any faulty gages to the factory. Gages should not be
opened in the field. For additional troubleshooting and support, contact Geokon.
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 Gage 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?
 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 gage? If not, it may have a low battery or
possibly be malfunctioning.
Symptom: Strain Gage Fails to Read
 Is the cable cut or crushed? Check the resistance of the cable by connecting an ohmmeter to
the sensor leads. Table 5 shows the expected resistance for the various wire combinations;
Table 6 is provided to fill in the actual resistance found. Cable resistance is approximately
14.7Ω per 1000' 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 gage 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 gage? If not, it may have a low battery or
possibly be malfunctioning.