Automated system for inductance realization traceable to AC resistance with a three-voltmeter method

An automatic system for the comparison of unlike impedances in the range 1 (ohm)-10 k(ohm), based on the three-voltmeter method, has been constructed and is undergoing extensive tests as a system for realization of the inductance scale at the Istituto Elettrotecnico Nazionale Galileo Ferraris (IEN), in the range 100 (mu)H-10 H at frequencies of 120 Hz and 1 kHz. The main features of the system are a two-phase direct-digital synthesis generator for energizing the standards, complete fourterminal pair definition of the standards with automatic servosystems, the use of a single high-accuracy voltmeter and a switching unit, and optical links for the distribution of frequency references. Measurements at the metrological level have been performed at 1 kHz with inductors in the range 10 mH-1 H