Abstract: The apparatus comprises a measuring unit (300) which receives a component to be tested (Cx) in series with a reference impedance in a measuring chain, a clock (100) suitable for applying repetitive stimulating pulses to the measuring chain, means for resetting the voltage at the terminals of the reference impedance to zero during each inactive half-cycle of the stimulating pulses, sampling means (400) which sample the response at instants which are progressively shifted relative to the stimulating pulses, and a processing unit (200) which analyzes the samples taken by the sampling unit to deduce the parameters of the tested item using a Foster model.