how can i measure inductance?

[hhoexclusive]

Have bought a new multimeter recently and today my 2 year old threw it out the back of my van onto the concrete. now my inductance setting doesn't work and i've just finished winding the inductor for my meyers setup dammit!!!. i have tested the new inductor and it works perfectly when a signal is pulsed thru it, But i need to know the inductance to work out what to set the frequency of my pwm at to get resonance. all the other settings on my meter are working fine and now i have no chance of getting a new one on warranty can i work out the inductance another way ? thanks in advance.

[Inquorate]

Inductance

Not that I know of, but gotoluc's videos on resonance to share thread show how neon lights up at resonance.

[Tehnoman]

The simplest way to do it is to use AC with known frequency together with variable resistor to determine coil impedance from Ohm's law, then use multimeter to determine it's active resistance, from that - coil's inductive resistance, and from AC frequency - inductance. Bear in mind, that if frequency will be relative low together with coil's active resistance relative high, result error will be quite high.

U - effective AC voltage over coil, I - effective AC current, Z - impedance, XL - inductive resistance, R - active resistance, f - frequency, L - inductance.

Z=U/I
XL = SQRT(Z^2-R^2)
XL = 2*PI*f*L
L = XL / (2*PI*f)

result - AVERAGE(L);

Better yet - if you have signal generator, measure impedance in respect to frequency. Accuracy would be way higher.

[Inquorate]

Inductance

Put your coil measurements into the calculator here. Remember spacing between wires = enamel or plastic coating of wire.

DeepFriedNeon - Tesla Coils

[Guest]

Buy an LCR-meter I suggest the HM8018 from Hameg, expensive but worth its money in the end. No need for further hassles...

[broli]

I would suggest tehnoman's technique. The online calculators are rubbish for personal projects as they apply to one very general coil setup. You would get much accurate results if you measure out your own impedance. But also remember that at high frequencies there's parasitic capacitance. Which may change the inductance value?

[Tehnoman]

That is true, these "theoretical" values of inductance will be even more away from actual value. Approximate value we can get out of it, but just in cases which are relatively simple. Like finite size cylinder-type coil. In that case the theoretical formula is:

L = mi0*mi*n^2*S/(h+0.45*d), where mi - core magnetic coefficient, n - wire turn count, S - area of coil's cross-section, h - coil's length (cylinder height), d - coil's diameter (cylinder diameter).

As for other configurations - in ideal toroidal case there is appropriate to use infinite long magnet inductance formula and that is it.

About capacitance - it exists at every frequency, but effect may show up only at higher frequencies. But in this case I doubt that parasitic capacitance would mess things up.