A precise standard of high capacitance

The four-terminal capacitance standard described uses two auto transformers to scale the value of a 1-μF capacitor to higher decade values up to 1 F. The direct-reading accuracy is ±0.25 percent at 100,120, or 1000 Hz. Much better accuracy is possible if the 1-μF value is precisely determined, because the scaling ratios are precise. Intermediate capacitance values can be obtained by using an external capacitor. The unit also acts as a standard of dissipation factor and is useful as a two-terminal capacitance standard up to 1000 μF at 100 or 120 Hz.