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Earth Resistivity Meter by John M. Stanley
This project is a simple earth resistivity meter. Although it is a four-probe design, it uses a simple DC voltage for generating the ground current instead of an AC current, so it is potentially affected by galvanic errors with the source probes.
This article was originally published in an issue of ETI magazine, and reprinted in the 1981 ETI book "How to Build Gold and Treasure Detectors."http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=geo&file=projects/erm2/index.dat
Earth Resistivity Meter by Robert Beck
This is a two-part article that gives the construction details for a device that can measure ground resistivity deltas. Such deltas might indicate buried anomalies such as large stones, compacted regions, or conductive targets. The articles also give a good background on resistivity measurement as well as some of the pitfalls to watch out for.
It was published in the January, 1997 issue of Everyday Practical Electronics, a popular British electronics magazine that is owned by publisher Wimborne Publishing, Ltd.http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=geo&file=projects/erm1/index.dat