Calibration of capacitance and dissipation factor bridges

A new method is presented for the calibration of capacitance and dissipation factor bridges. These bridges form the values indicated by them from the complex ratio of their input currents. For calibration, two sinusoidal AC currents are synthesized with the aid of a digital, programmable two-channel AC voltage source and two AC resistors and fed into the bridge. The complex ratio of these synthesized input currents is calculated from the AC voltage ratio determined by a sampling method, and from the impedance ratio of the AC resistors. At currents of about 5 mA, their ratio at frequencies of about 50/60 Hz can be exactly realized and measured with uncertainties of less than 1/spl times/10/sup -6/ or 1 /spl mu/rad.