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, such as ultrapure 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 presented here. The spectrometer defines the impedance under measurement as a two-port standard and measures impedance spectra covering 5 dec, reaching frequencies in the millihertz 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.