Preliminary Study of a Nonbridge Method for Precision Measurement of Capacitors at Low Frequencies Using Operational Amplifiers and Resistance Standards

High-precision measurements of capacitance and dissipation factor can be made without capacitor standards using active circuits known as gyrators, which are constructed with high-gain operational amplifiers and precision resistors. A theoretical analysis of the technique is carried out here using one particular gyrator circuit. A preliminary experimental study yielded values of dissipation factor, which agreed with measurements made by the manufacturer of the precision capacitors tested to within four parts per million. The theory suggests that with a more carefully engineered instrument, capacitors of 0.01-1 ??F in the 10-1000 Hz range may be measured with an accuracy of the order of 1-2 ppm. The accuracy appears to be determined primarily by the precision of two critical resistors in the gyrator.