Self-compensating networks for four terminal-pair impedance definition in current comparator bridges

The four terminal-pair definition of standards allows to reach ultimate accuracy in impedance metrology. The four terminal-pair definition requires dedicated circuitry to be included in the bridge network, and the reach of auxiliary bridge balances during the measurement. A careful choice of the network topology allows the bridge to be self-compensating: the four terminal-pair definition is in large part achieved by the behaviour of the network itself, without any adjustment. The additional circuitry required for impedance definition can therefore be simpler, the balancing procedure becomes easier, and a more robust four terminal-pair definition is achieved. This paper analyses a current comparator bridge network with a topology featuring self-compensation. A digitally-assisted test implementation was realized; test measurements on ac resistance comparison in the 25 ohm to 100 ohm range, at kHz frequency, are reported.