A resistivity measuring system using a “lateral” electrode configuration. A constant current is passed between an electrode A on the bridle and a distant electrode B, while the potential difference is measured across two electrodes, M and N, located on the sonde. The MN distance is small compared to the AO spacing, which is the distance between the current electrode and the midpoint between the potential-measuring electrodes, typically about 18 feet 8 inches. A short lateral sometimes uses a spacing of 6 to 9 feet. The potential electrodes described above are located below the current electrodes, but on the reciprocal sonde the functions are interchanged so that potential electrodes are above the current electrodes. The measure point is the midpoint between the two electrodes separated by the shortest distance (i.e., MN electrodes; or, AB electrodes on the reciprocal sonde).
The lateral device has a deeper depth of investigation than the normal devices with which it is generally used, but has the disadvantage that it requires thick homogeneous beds for optimum usefulness and produces an unsymmetrical curve.
