current senses is a direct reflection or function of the pad impedance of the corresponding pad contact pair 18 a 18 b according to the physics of a series resonant network each series resonant network 44 a 44 b is an rcl network or a combination of r resistance l inductance and c capacitance in a preferred embodiment of the series resonant networks 44 a 44 b the inductive component for each network is integrated into the respective transformer 38 a 38 b the frequency response of a series resonant network has a maximum resonant frequency f r at the resonant frequency the series resonant network has the minimum impedance as opposed to a parallel resonant network which has the maximum impedance at the resonant frequency and the phase angle is equal to zero degrees the total impedance of a series resonant network is z t jx l u2212 jx c r j x l u2212 x c at resonance x l x c f r 1 2 u03c0sqrtlc z t r and v l v c the resonance of a series resonant network occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are 180 degrees apart in phase the left and right current senses are applied to pad contact impedance measurement subsystem 46 which determines whether the impedance measurements between pads or return electrodes.