Troubleshooting - Geokon 4820 Instruction Manual

5. TROUBLESHOOTING

Maintenance and troubleshooting of Vibrating Wire Pressure Cells is confined to periodic checks
of cable connections. Once installed, the cells are usually inaccessible and remedial action is
limited. Consult the following list of problems and possible solutions should difficulties arise.
Consult the factory for additional troubleshooting help.
Symptom: Thermistor resistance is too high
 Likely, there is an open circuit. Check all connections, terminals, and plugs. If a cut is
located in the cable, splice according to recommended procedures.
Symptom: Thermistor resistance is too low
 A short is likely. Check all connections, terminals, and plugs. If a short is located in the
cable, splice according to recommended procedures.
 Water may have penetrated the interior of the transducer. There is no remedial action.
Symptom: Pressure Cell 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? Try reading the cell on a
different readout position. For instance, channel A of the GK-404 and GK-405 might be able
to read the pressure cells. To convert the Channel A period display to digits use Equation 2.
  Is there a source of electrical noise nearby? Most probable sources of electrical noise are
motors, generators, transformers, arc welders, and antennas.
 Make sure the shield drain wire is connected to ground. Connect the shield drain wire to the
readout using the blue clip. (Green for the GK-401.)
 Does the readout work with another pressure cell? If not, the readout may have a low battery
or be malfunctioning. Consult the appropriate readout manual for charging or troubleshooting
directions.
Symptom: Pressure Cell Fails to Read
 Is the cable cut or crushed? This can be checked with an ohmmeter. Table 3 shows the
expected resistance for the various wire combinations; Table 4 is provided for the customer
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 reads very high or infinite (megohms), a cut wire must be suspected. If the
resistance reads very low (<100Ω), a short in the cable is likely.
 Does the readout or datalogger work with another pressure cell? If not, the readout or
datalogger may be malfunctioning. Consult the readout or datalogger manual for further
direction.
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