Hand held impedance measurement system with seven decade capability and potentiostatic function

This paper describes design and test of a new impedance measurement system for non-linear devices that exhibits a seven decade range and works down to a frequency of 0.01 Hz. The system is specifically designed for electrochemical measurements so that it can work with a few millivolt stimuli still compensating electrochemical voltages of several volts, but the proposed architecture can be employed in many other fields where a flexible signal generation and analysis is required. The system employs an unconventional signal generator based on two PWM oscillators and an autocalibration system that allows uncertainties of less than 3% to be obtained over a range of 1 KΩ to 100 GΩ. A synchronous demodulation processing allows the noise superposed to the low amplitude of the employed signals to be made negligible. The proposed system is able to work either as a stand-alone device or in connection with a personal computer. In this latter case, thanks to the instrument internal architecture, the personal computer can set almost any parameter, has access to the raw required data and can implement new data processing and analyses.