Calibration of High-Voltage Current-Comparator-Based Capacitance and Dissipation Factor Bridges Using Nonsynchronous Sampling

An alternative approach for calibrating automated high-voltage current-comparator-based capacitance and dissipation factor bridges is presented. For the calibration, two sinusoidal currents are synthesized with two synchronized signal generators and two resistors and injected into the bridge inputs. The capacitance ratio and dissipation factor simulated by these currents are calculated from an ac voltage ratio estimated from the digitized data, together with the impedance ratio of the resistors. The approach is a refinement of another approach previously published that leads to larger uncertainties but is slightly easier to implement since the digitizers need not be synchronized to the signal generators. It is possible to simulate capacitance ratios ranging from 1 : 1 to 10 : 1 with relative standard uncertainties of less than 2.0 middot10^-5 and dissipation factors ranging from 0 to 0.1 with standard uncertainties of less than 1 middot10^-5.