Generally, the instrument for measuring inductance is to connect the inductance to be measured and the capacitor with known capacity into an LC oscillation circuit, let them produce series resonance, and then measure the oscillation frequency. Using the formula f = 1/[2 π× (l× c)-2], the inductance can be calculated.

Transforming the measurement of inductance into the measurement of frequency makes the measurement simple, because the measurement of frequency is very easy and there are many methods, such as:

The sinusoidal AC signal generated by oscillator oscillation is shaped into a square wave signal by Schmidt trigger, and the time interval between two rising edges of the square wave signal can be measured.