Impedance measurement technique based on sine-fit

An impedance measurement system that is based on a voltmeter with digitising capabilities and on a sine-fit processing is proposed in this paper. The system can be arranged by employing standard instruments that are commonly available in calibration laboratories for the measurement of other electrical quantities. Two different solutions are proposed that differ in the used standards. One solution employs a multifunction calibrator that feeds the unknown impedance and a digital multimeter that acquires the voltage signal across the impedance; the other solution employs the same digital multimeter and a standard resistor in order to estimate the current that flows through the unknown impedance. In both cases the acquired samples are processed according to a four-parameter sine-fit algorithm. The system the authors have arranged allows impedance measurements in the frequency range of 40 Hz to 5 kHz to be obtained with expected standard uncertainty of about 0.04 % on the amplitude and of a less than 0.06 º on the phase.