Design and Implementation of a Low-Frequency Current Comparator Bridge Based on Quantized Hall Resistance

Quantumized Hall resistance (QHR) provides a traceable absolute reference for resistance measurement. However, the traditional transfer system based on super-conducting current comparator (CCC) relies on cryogenic liquid helium environment, which is complicated to operate and expensive. In this paper, a wide-range QHR transfer bridge scheme based on room temperature low-frequency current comparator (LFCC) is proposed and implemented. The system works under low-frequency AC excitation (<10 Hz), uses high-precision active/slave current sources to drive precision proportional windings, and achieves flux balance through detection windings and resonant amplifier feedback loops, thereby achieving high-precision resistance value transfer. The LFCC core magnetic circuit model, detection sensitivity model and closed-loop control model are established, and the proportional transfer relationship and error source are derived in detail. An experimental device including multi-layer magnetic shielding proportional windings, low-noise current sources, high-Q resonant detection amplifiers and digital control systems is designed and constructed. Experimental results show that under room temperature conditions, the LFCC bridge can achieve a proportional transfer uncertainty (k=2) better than 10⁻⁸ in the 1kΩ range. This solution gets rid of the dependence on liquid helium and has a relatively simple structure. It provides an effective technical approach for wide-range and high-precision resistance calibration in new power systems and has significant engineering application value.