A three-arm current comparator bridge for two terminal-pair impedance comparisons over the complex plane

A three-arm current comparator impedance bridge is here presented. This bridge is digitally-assisted, and allows comparisons among three unlike impedances, defined as two terminal-pair standards. Its scope is the calibration of impedances having arbitrary phase angles, against calibrated nearly-pure impedances. Preliminary tests, the measurement of an air-core inductor and of an RC network versus decade resistance and capacitance standards, at kHz frequency, are presented; the relative deviations respect to well-established calibration methods are in the 10^-5 to 10^-6 range, with potential for improvements.