This page gives the equation for air core inductors, which is essentially the same as the ones given earlier. The changes in coefficients are due to change in measurement units.

https://www.allaboutcircuits.com/textbook/reference/chpt-1/inductor-sizing-equation/

 

You can try using any low frequency square-wave pulse into L and C parallel resonance circuit.
View attachment 155772
Measure the period of the damped oscillation.

View attachment 155770
With C = 100nF and L = 1000nH,
resonance frequency = 500kHz, period T = 2μs
Very doable on an oscilloscope.

C = 100nF and L = 600nH
f = 650kHz
T = 1.54μs

Hi there,

I just noticed this post and the formula given that must be w=1/sqrt(LC).

I thought you would want to know that this kind of test would yield a formula as:
w=sqrt(L*(4*C*R^2-L))/(2*C*L*R)

and this shows some dependency on the value of R while w=1/sqrt(LC) does not.

The difference lies in the value of R, and is sort of relative to the value of L as to how small it is.
So sometimes it does not matter, but sometimes it will change the value by hundreds of percent.
For the example of 1uH and 100nF, for R=5.06 Ohms the two formulas are within 5 percent of each other, while for R=2 the two formulas are within only about 40 percent of each other. Although not as interesting, for R=1 we dont even get an underdamped response
Luckily, with a more reasonable R=50 Ohms the two agree to within 0.5 percent (one half of one percent) which nobody would argue is not acceptable (as it certainly would be acceptable for most cases).
That is for the above example L and C, but for other L and C it would have to be recalulated and a reevaluation performed.

I just thought you would want to be aware of this difference in formulas for the said circuit.

 

So I did some measurements. Between 0 and rise, the time was around 9 microseconds, 63% off that is 5.67. My resistor's value was 691K, so 691000*0,00000567(5.67 microseconds)=3,91797. How should I interpret this number? The expected value of the coil should be 0.00000121(lets add 5-10% error on that one) nanohenry.

Since the connections themselves can be in the 20nH each (for a hole-through type), what you try to measure is just too small, I am afraid, since your montage will introduce more inductance than the coil-thing that you try to measure.

Unless you come with a solution involving two measurements with the same montage, one without the coil to be measure and one with it, to get two equations with two unknowns ( the capacitance of the montage and the capacitance of the coil to be measured), and assuming that this set of equations is not too "sensible" to errors, I don't think that you can really get a solution with standard equipment available to hobbyists :-(

 

First off -- bravo for trying the experiment!

The capacitors you tried using are pretty big, and I wonder if you've actually measured _them_ somehow to verify their values?

Also, large capacitors like that may have bad to very bad high frequency performance, so you may actually be measuring not with the "C" of your capacitors, but with the parasitic capacitance of your setup (which will be relatively small) while your actual capacitor is acting more like an
an open circuit. If you start by assuming your 100uH inductor is accurately labeled, what capacitance would it have to be working with to give you that 1.5MHz ring?

Let us know what you discover!

 

WAKE UP! Unless this is some kind of school assignment don't get off in the weeds like what is happening here!
For 20 bucks get one of these:
https://www.ebay.com/itm/New-LC100-...=inductance+capacitance+meter&_from=R40&rt=nc

It measures down to 1/10 microhenry and can be zeroed to get rid of test lead inductance. It does a very nice job of measuring small value RF inductors like you apparently are trying to measure.

 

Or for another $2 get https://www.ebay.com/itm/Mega328-Tr...LED-Diodes-Transistor-Resistance/352306573353 to test and identify anything. I'm not sure how accurate it is on inductance but for general usefulness, it can't be beaten IMHO.

Derek

 

(…) I'm not sure how accurate it is on inductance (…)

Derek

Someone may wish to test it, would it be just ONCE, to trust the tool, with an oscilloscope, as example Very interesting gadget though! Thanks for the link.

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