An a.c. low resistance bridge
M.C. McGregor · Journal of Scientific Instruments · 1966
The bridge described is for the measurement of low values of resistance. It has three ranges, 10, 100 and 1000 mΩ, an accuracy to 0.1%, and at maximum sensitivity 0.1 μΩ can be detected. The unknown and reference resistors are connected in series with a mains frequency (50 Hz) source. The voltages at the potential terminals of the resistors energize two transformers which provide the ratios and decade adjustments for balance. A phase-sensitive detector is used to indicate balance and the meter is scaled to read directly the resistance unbalance.