A Current Comparator Based Four-Terminal Impedance Bridge

This paper presents a current comparator based four-terminal impedance bridge for quantity-value dissemination of national AC resistance standard in China. In order to enhance the feedback adjustment ability and simplify the balance process, the bridge applies a frequency selective amplifier instead of feedforward and feedback networks to balance the magnetomotive force of the current comparator. The resistance difference between the measured and standard resistor can be calculated according to their voltage difference indicated by a digital lock-in amplifier. The AC/DC resistance relative differences between Double Helix Resistor and Tinsley standard resistor are measured with the proposed bridge under 1592Hz.