# Joule Thief: Supplement: Determining Inductance by Resonating a Tank Circuit

Here I illustrate the basic procedure for determining an unknown inductance value.

A known capacitor of high quality is selected, and the inductor and cap are connected together in parallel. A Function Generator set to make a square wave output is connected across the tank, as are a scope probe and a frequency counter probe. The FG is swept until the resonant frequency of the tank is found. Then the capacitance and the frequency are entered into an on-line calculator and solved for the inductance of the coil.

The errors will arise from inaccurate identification of the frequency at which the peak voltage occurs, and in the value of the capacitor chosen. Still…. I arrive at a figure that agrees with the reading of both a commercial inductance meter and my Arduino-based inductometer, to within 10 percent error or better.

On-line calculator used:

http://www.1728.org/resfreq.htm

Also used:

Tektronix 2213 scope

Philips PM6676 counter

Interstate F43 function generator

1 uF poly film capacitor