Primary measurement method for the characterisation of impedance standard in the mΩ range

Impedance standards having impedance values in the low mΩ range, with non-zero reactances, and operable with alternating current-currents of a few Amps and up to a few kHz are needed for appropriate impedance meter calibration. These challenging operation parameters are most relevant for electrochemical impedance spectroscopy of high energy Li-ion battery cells. We present a primary measurement method that can be used for the characterisation of respective impedance standards traceable to the SI. Basically, two calibrated high precision DC voltage meters are used to sample the voltages across a characterised reference resistor and the impedance standard under test, while both are excited with the same ac current. The measured voltages are fitted with sin waves and the complex impedance value is calculated from the amplitudes and phase difference of the voltage curves. We present the measurement results of a test impedance in mΩ range, including a full uncertainty budget. Moduli of the measured impedances are compared with those of another method that has been presented recently. The results are equivalent up to 1 kHz and within a relative expanded uncertainty of around 0.47%.