Résumé
We present an experimental study on a.c. measurements at low frequency (below 1MHz), when coaxial cables used for the measurement are resistive, as in cryogenic conditions. More precisely we are interested in admittance or impedance measurements and the accurate determination of the phase. Our experiments were completed using an auto-balancing bridge impedance analyzer and various standard coaxial cables as well as their serial combinations. We characterize experimental setup, then we analyze and measure the phase shift introduced in impedance measurements by leads resistance. Using basic equations for electrical signal propagation in coaxial cables, we calculate phase shift in the whole frequency range and explain our data in the low frequency limit of our model. We propose a quantitative criterion to determine whether the experimental context is appropriate. If not, we show that by using an original calibration procedure the imaginary part can be accurately recovered, avoiding artifacts. The calibration procedure can be applied to any a.c. voltage or current measurement, whatever the detection technique, with known accuracy.