IN3LBQ on the Hühnerspiel (Amthorspitze) - photo by IN3OTD

Inductor Capacitance and Inductance Estimation

To be able to estimate the parasitic capacitance effects on an inductor you need to do (at least) two measurements, because with one measurement we can only determine one parameter. The simplest way to do this is to resonate the inductor with two different capacitors in parallel and measure the two resulting resonance frequencies; for this purpose, a grid-dip meter or a simple oscillator can be used. With the two measured resonant frequencies and the two known capacitance values we can estimate both the true inductance and the distributed capacitance. Note that, to determine the inductance, only the difference between the two values of capacitance and not their absolute values needs to be known. That means that you can at first resonate the inductor at a convenient frequency with any capacitor you find at hand, and then shift the resonance adding in parallel a low-tolerance capacitor to get a good estimate.
If you know precisely both capacitance values (that means knowing also the parasitic effects from the fixture, oscillator, wiring, etc.) you can obtain also an estimate of the inductor parallel capacitance.
The modeling of an inductor as an ideal inductance in parallel with a capacitance is valid only at low frequencies. A complete model will have an infinite number of parallel LC resonators connected in series.[1]


First Frequency,  f1 :  MHz
Second Frequency, f2 :  MHz
First Capacitor,  C1 :  pF
Second Capacitor, C2 :  pF


Inductance Value,  L :  µH
Capacitance Value, C :  pF


[1] B.A. Anicin, D.M. Davidovic, P. Karanovic, V.M. Miljevic, V. Radojevic, "Circuit properties of coils," IEE Proceedings, vol. 144, no. 5, Sep. 1997.