Computer controlled multielectrode impedance measurement system

The four electrode methodology for measuring electrical resistivity at low radiofrequency is a well established technique and has been documented extensively in the literature. Current is passed between the outer two electrodes of a linear four electrode array and the induced voltage between the two inner electrodes is measured. The circuitry that is associated with these measurements is generally easy to construct. In practice, however, real interest lies in making anisotropic resistive measurements of a medium. Furthermore, many applications require that measurements be made continuously to observe dielectric changes over a finite period of time. This paper presents a practical approach for making continuous anisotropic four-electrode measurements