Add to ORKGThe alternating current potential drop method (ACPD) with four-point probe injects alternating current into the sample under test from the two outer drive pins and measures the voltage (potential) drop between the two inner pick-pins. This method can be used to measure electrical conductivity, linear permeability, coating depth, as well as crack size. However, the measurement speed and accuracy of present ACPD system need to be dramatically improved. This work discusses the design, implementation and test of a novel ultra-fast standalone ACPD system. New and powerful hardware including high current transconductance amplifier and low noise amplifier provide a sound foundation for nearly perfect system level noise performance; new time domain...