New Automated Coaxial AC Bridge for Rapid Calibration of AC Resistors

A new automated coaxial AC bridge 10:1 for the calibration of AC resistors from 0.1 O to 100kΩ in the frequency range from 50 Hz to 10 kHz has been fabricated by Japan Electric Meters Inspection Corporation (JEMIC). The distinguishing feature of our new AC bridge is that no injection signals are required to balance the bridge circuit, that is, the voltage difference is read directly. The system is computer-controlled using a coaxial mechanical scanner for setup, and it is only necessary to select 'start' on a PC. As a result, it takes less than one minute to calibrate an AC resistor. That is, our new method enables rapid calibration of the AC bridge. The AC bridge has been evaluated by using calculable resistance standards and by comparing it with a conventional AC bridge at JEMIC. The relative expanded uncertainties of the present system have been estimated to be 15×10-6 for the in-phase component and 30×10-6 for the quadrature component at 1 kHz.