A current comparator bridge for measuring the value of an unknowncapacitor includes a current comparator having a first comparator windingwith an adjustable tap which is connected to one side of a standard capacitorand a second comparator winding connected to one side of an unknowncapacitor, a high voltage source being connected to the other side of thecapacitors. The current comparator is provided with a detection winding fordetecting when the ampere-turns in the first and second comparator windingsare equal and opposed to each other. In addition to the current through thestandard capacitor being applied to the first comparator winding, the bridgeincludes a circuit to add a current through a standard conductance to the firstcomparator winding as well as circuits to compensate for errors. Thedetection winding is connected to a current-to-voltage converter with an adjustablegain which provides a signal to a phase sensitive detector. A reduced replicaof the high voltage source is also applied to the phase sensitive detectorwhich provides output signals Eo and Eqo to indicate when the bridge isbalanced for both in phase and quadrature components respectively.The values of the capacitance and dissipation factor for the unknowncapacitor can then be determined from the balanced condition of the bridgewhich is designed so that it can be automatically controlled by amicroprocessor and switch controller.
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