Versatile four-probe ac conductivity measurement system

The design of a four-probe ac conductivity measurement system is described. The system is capable of making precision conductance measurements from 10(-8) to 10(-5) S at 20 to 200 Hz. Driven coaxial shields and a controlled current source are utilized to eliminate phase shift/attenuation errors, and make the measurement of conductances on a variety of materials a routine procedure requiring a minimum of operator intervention.