A MICROCONTROLLER-BASED SCHEME FOR MEASUREMENT OF L AND C

A scheme for the measurement of component values of inductors and capacitors is described. In this scheme the inductor or capacitor is connected in series with a known standard resistance and this series circuit is excited by an Ac voltage source with appropriate amplitude and frequency. The phase differences between the supply voltage, voltage across the inductor/capacitor and the voltage across standard resistance are measured using a microcontroller. The governing equations giving the unknown inductance or capacitance are evaluated by the microcontroller. The technique is independent of the voltage across or current through the unknown inductor or capacitor. Because the excitation frequency is measured by the microcontroller, tests can be carried out at a desired frequency. The uncertainties in the measurement increase with the applied frequency for a given clock frequency of the microcontroller. The proposed scheme was implemented based on an INTEL 8751 microcontroller. For the prototype built, with a one decade span in the measurement range, an accuracy of +/-0.4% has been achieved.