Method and apparatus for diagnosing faults in the geophone group of a geophysical data acquisition system

Apparatus for fault diagnosis of a geophone group within a geophone group-cable complex of a geophone data acquisition system which employs extensive series-parallel networks of geophones spread over the earth's surface and in which electrical signals from said groups must traverse along an extended geophone cable in order to be collected, detected and recorded, said apparatus looking electrically through said cable toward said group under test and yet compensating electrically for resistive effects of said cable to detect and possibly identify faults within said geophone group under test and among geophones within each group, comprising:

• a. means for injecting into an input of said group-cable complex a DC current of predetermined amplitude,
• b. means for injecting simultaneously into said input of said group-cable complex an AC current of peak absolute amplitude equal to said amplitude of said DC current, and
• c. means for detecting and measuring excess of (i) peak voltage produced by injection of said AC current, over (ii) DC voltage generated by injection of said DC current at said input of said group-cable complex, said excess being a measure of a difference between AC and DC impedances of said geophone group under test independent of said cable through which said DC and AC currents are driven.