Dear Nick e.t. all,
Thanks so much for creating such a versatile tool. I got a Tsunami board to measure inductors and capacitors, but am struggling with how do this. I found your excellent post on measuring component networks Howto part 5: Measuring component networks. It gets me very close to getting a typical component value for the inductor or cap, but ends with “with a little number crunching we could easily compute the inductor's value…” I am trying to figure out the math involved with process. Is the process described at the following link the correct method? Impedance Calculation If not, can you help me with the final calculation?
Thanks so much,
That page looks correct, yes.
In practical terms, what you need to do is derive an equation for the equivalent circuit you're measuring - which might be as simple as a single ideal inductor, or might contain multiple parasitic terms - then perform linear regression to match it to your observed curve as closely as possible.
For instance, Wikipedia gives the voltage across an inductor as V(I) = 2 * pi * f * L * I. The inductor's in series with the Tsunami's built in 50 ohm load resistor, which follows ohm's law V(r) = I * R. Knowing this, and knowing the input voltage (V(i) + V(r)) and the output voltage (V(i)) and the frequency (f) at each point, you can generate a curve for a given inductance that should match the measured one. If no curve matches, your equivalent circuit is incomplete - there are other parasitic or physical components not accounted for.