An impedance spectrometer for the metrology of electrolytic conductivity

Conductivity measurements of liquids ask for measurements of impedance spectra in a wide frequency range to identify stray parameters caused by electrode-surface effects. On low-conductivity liquids, like ultra-pure water, frequencies of interest range below those available on precision LCR meter (usually in the 10 Hz range). A new impedance spectrometer based on multifrequency excitation and discrete Fourier transform analysis is here presented. The spectrometer defines the impedance under measurement as a two-port standard, and measures impedance spectra covering 5 decades, reaching frequencies in the mHz range. The instrument accuracy is verified by measurements on calibrated resistance standards. As an example of application, measurement results on pure water samples and a comparison with measurements performed with an LCR meter are reported.