Expand Capacitor and Inductor Frequency Range Using a Dependent Correction

Abstract

Impedance is the opposition to alternating current flowing in an electric circuit or component. Impedance is expressed in basic circuit elements that include resistance (R), inductive reactance (XL), and capacitive reactance (XC). Real-world components are made up of wires, connections, conductors and dielectric materials combine to make up the impedance characteristics in a circuit. Impedance can change due to signal frequency and voltage level, the presence of a DC bias voltage or current and environmental factors such as operating temperatures or altitude. Of these potential influences signal frequency is often the most significant factor. Most commercial LCR bridges and meters have the capability to make measurements with selectable test frequencies. This feature is important because to obtain accurate measurement results the test frequency should be very close to the desired operational frequency. National Measurement Institutes typically provide traceable values at 1 kHz and 100 Hz, as default option. In order to use a capacitor or inductor over its entire frequency range an additional process is needed. This paper describes a method to determine and use a frequency correction factor to calculate the actual capacitance or inductance values over their entire frequency range using a commercial LCR bridge. Calculation of the uncertainty component associated to the frequency correction factor is included as well as the effect in the calculations of the capacitor or inductor accuracy.