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Originally Posted by Theseus
Certain frequency????
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My guess: more than 1 Hz, less than 10 Khz. Probably in the audio range, maybe 400 Hz.
Voltage - My guess: More than 1.5 v, less than 250 v. Probably between 6 and 12 v.
Ground resistivity has been measured by many experimenters and geologists. I have read reports of DC being used from a 12v automotive battery to check current flowing between copper rods driven into the ground at spacings from a few feet, to over a hundred feet. I have also read reports of over 1000 volts being used to test longer distances, where the negative rod was driven in a reference location, and test rods on the positive terminal placed at various locations to survey the relative resistivity of the soil. This technique is also used to test signals used for induced polarization, and other related ground surveying methods.
In Esteban's example, the objective is to make a portable hand-held device for quick, convenient field tests. This would require using low power disposable a battery powered tester. If low voltage probes are used, then it is necessary to cancel the current caused by any telluric currents in the test area that might skew the readings from the tester. Using an oscillator will allow testing the current flowing in both directions (polarities) to yield an average current flow while ignoring the DC portion that comes from outside sources in the ground. With the proper circuitry, you could also detect the DC component, indicting the flow of telluric current.
You can read more about how to measure ground resistivity in the geotech sections of the forum as well as websites dedicated to geological testing methods. Much is written.
Best wishes,
J_P
ps. Seems I posted too late. Esteban finished his reply before I submitted my guess
