Measuring Inductance

[aniket]

Hi all,
I was measuring a inductor at 1Khz/1V and it showed me a inductance of 5mh , but when i changed the test parameter to 1kz/0.250V the inductance changed to 12mh .. DCR of the inductor is 0.4E . I repeated the same test with a smaller inductor of 10uh and its measured inductance stays same irrespective of the test parameter ...why is this happening with the bigger inductor is my test equipment faulty ?? or am I measuring incorrectly ?

Regards

[T3sl4co1l]

Core permeability varies as a function of flux density (Bmax).  Sounds like it's near saturation.

Bmax is a rather useless parameter, because you have to know core dimensions and number of turns; it's not something where you can simply apply a known waveform and say it's now running at so-and-so flux density.  But anyway, those are the missing parameters, and the rest is just ratios, so it's not like it's some mysterious property.

1kHz may also be rather low to be testing at.  Though a reactance of ~30 ohms compares favorably to the 0.4 ohm DCR, so it shouldn't be too bad.

If reactance were smaller, it would be that much more important that your inductance meter performs a meaningful measurement.  (Many testers simply measure the magnitude of the AC voltage or current developed -- capacitor ESR testers very commonly do this -- and so do not take into account the ratio of reactance to resistance.)

Tim

[danadak]

Here is a project using synchronous detection for Z measurement. Cypress PSOC. IDE
is "Creator", free, just download it. Note this particular project uses an older version
of Creator, not sure which one, maybe 3.0. So you would need to download that to
open and compile the project. You could then update it at a later time to run with the
current version of Creator, 4.0. Or ask the Cypress team to do the update with a post
to tech support forum.

http://www.cypress.com/products/psoc-creator-integrated-design-environment-ide


https://www.dropbox.com/s/6s7c58fbartcakd/Phoenix%20Impedance%20meter%20project%20and%20info%20HighSpeed%20-%20Copy.zip?dl=0


And this might be useful -


http://cp.literature.agilent.com/litweb/pdf/5950-3000.pdf       Agilent Z Measurement Handbook


Regards, Dana.