How to measure low inductance

[jarodtufts]

Help please.  I'm getting a bit frustrated trying to find an affordable LCR meter that will measure low inductance for a project that I'm working on.  I have to wind my own inductors so I want to test them before I install them.  They are in the range of 140nH to 3uH.  It seems that all affordable meters bottom out at 20uH (i.e. MASTECH MS5308 or IET DE-5000).  Any suggestions?

[David Hess]

The IET DE-5000 has a resolution of 0.001uH or 1nH on its 20uH range albeit with 2.5%+5 accuracy.  With kelvin clips and calibration, isn't that good enough?

[jarodtufts]

The IET DE-5000 has a resolution of 0.001uH or 1nH on its 20uH range albeit with 2.5%+5 accuracy.  With kelvin clips and calibration, isn't that good enough?

That would be good enough.  Maybe I am misunderstanding the spec sheet.  When it says "Range 20.0uH / Resolution 0.001uH".  Does that mean "From 0 to 20uH", or does that mean "from 20uH to the next range"?

[tatus1969]

I have a UNI-T UT612, this can do up to 100kHz test frequency and has 1nH resolution. This one is quite affordable and I am very satisfied with it.

[David Hess]

The IET DE-5000 has a resolution of 0.001uH or 1nH on its 20uH range albeit with 2.5%+5 accuracy.  With kelvin clips and calibration, isn't that good enough?

That would be good enough.  Maybe I am misunderstanding the spec sheet.  When it says "Range 20.0uH / Resolution 0.001uH".  Does that mean "From 0 to 20uH", or does that mean "from 20uH to the next range"?

It means a measurement from 0 to 20uH with a resolution of 0.001uH or 1nH.  The next range up is 0 to 200uH with a resolution of 0.01uH or 10nH.

[jarodtufts]

The IET DE-5000 has a resolution of 0.001uH or 1nH on its 20uH range albeit with 2.5%+5 accuracy.  With kelvin clips and calibration, isn't that good enough?

That would be good enough.  Maybe I am misunderstanding the spec sheet.  When it says "Range 20.0uH / Resolution 0.001uH".  Does that mean "From 0 to 20uH", or does that mean "from 20uH to the next range"?

It means a measurement from 0 to 20uH with a resolution of 0.001uH or 1nH.  The next range up is 0 to 200uH with a resolution of 0.01uH or 10nH.

Thank you for clarifying that for me.  I purchased the MASTECH MS5308.  It is measuring my hand-made 3uH inductor very accurately.  in the nH range I'm getting readings that are close to what I expect, but the values move around quiet a bit.  I am suspecting my measurement method right now.  I'm going to try cutting the leads closer to the core.  I'm suspecting at the very low range that the lead length might be an issue.

[oldway]

As I measure small inductances that quite seldom, I use the parallel resonant circuit method.

I connect a precision capacitor of 100 or 470pf in parallel with the unknown inductance and I feed this resonant circuit with my high frequency generator through a 4k7 resistor.

I am looking for the resonance frequency (maximum voltage) and calculates the inductance .... the resonance frequency is known as well as the value of the capacitor, which allows to calculate the value of the inductance.

I use the probe X10 of my oscilloscope and I take into account the input capacity of my probe.