First post to the FB group Ferrite Antenna
My first experience with measuring inductors came a few years ago when I bought an LC IIb meter from AADE. It’s a very accurate meter but has a few quirks.
I bought a bunch of small 100 uH chokes from a US company, and when I got them I measured one and it measured 78 uH. What?! That’s way too low! So I measured a bunch more and they all measured below 82 uH, way too low. So I contacted the company and explained what had happened. They agreed to a refund if I sent them back. Later their tech emailed me. When the guy got them, he measured them with various inductance meters, high quality ones like Hewlett Packard. The inductors all measured low, some were close to 100 uH but still out of tolerance. He couldn’t explain why the inductors were so far off, and why the different meters gave different measurements. But I did get my refund.
The only explanation I have is that the various inductance meters use different frequencies for measuring on the same range. As the frequency varies, the inductor’s material, such as ferrite, changes its magnetic property and the result is a different measurement.
The one way to get a meaningful measurement is to put a 1 percent tolerance capacitor in parallel with the inductor and find its resonant frequency. Then calculate the inductance using the frequency and the capacitor’s value.
The moral of the story is you can’t always trust an inductance meter to be accurate with every inductor.
Also, many inductance meters cannot measure very low values of inductance. Some meters are not accurate below some value, such as 100 uH or 10 uH. Many coils that experimenters hand wind are smaller than these values, so they won’t be measured accurately, or won’t measure at all.
