[Lowfer] Measuring inductors

[rick kirby]

 Thanks Ed,

 Im dealing with torroid forms. Ive been using an oscillator circuit for a
while now which does ok with iron core or low value ferrite.I tried winding
a 100uh torroid the other day on a ferrite core.The oscillator has 2 test
positions.One position uses 27 pf and the other 174pf to resonate the coil
under test.When I tested the coil I wound using the 174pf cap the frequency
read 770khz which worked out to about 240 uh.When I used the 27pf cap I read
2.3mhz whichI think worked out to be around 180uh? When used with iron core
or lowr value inductors, those caps usually give me a reading within 10%.So
something it doesn't like about ferrite which is why I want to try a
different test setup.

 Thanks Again

            Rick  "PBO"





-----Original Message-----
From: lowfer-bounces at mailman.qth.net [mailto:lowfer-bounces at mailman.qth.net]
On Behalf Of Ed Phillips
Sent: Wednesday, March 09, 2011 01:46
To: Discussion of the Lowfer (US, European, & UK) and MedFer bands
Subject: Re: [Lowfer] Measuring inductors


I use a Q meter or audio frequency impedance bridge.  What kind of 
ferrite cores are you talking about?  Toroidal? E-I? What kind of 
ferrite?  Ungapped cores can exhibit saturation effects [increasing 
inductance with applied voltage] even at fairly low input voltages.  I 
have also have an AADE L/C meter:

   http://www.aade.com/lcmeter.htm

which also works well and is in my opinion well worth the price.  
Unfortunately when you're dealing with coils with 'ferromagnetic cores' 
saturation effects will always be present to some extent and measuring 
with intended operating voltage and frequency [and DC current if any] is 
necessary if you want really accurate results.  Usually tough to do.

Ed

rick kirby wrote:

> Hi All,
>
> Im looking for suggestions for accurately measuring ferrite and iron 
> torroids. I have been using a simple oscillator setup with a frequency 
> counter and a calculator.It has worked so-so with iron core coils but 
> with ferrite cores and inductances up in the hundreds of microhenries; 
> its
> all
> over the place.Maybe core saturation or something ; Im not sure. I have a
> scope ,counter, DMM and a cheesy little signal generator to work 
> with.I have
> heard mixed reviews on the commercial meters; the chief complaint 
> being they
> test the inductors at an audio frequency.I built an  adapter for the
> multimeter using a 74hc132 or something like that  and wasnt happy 
> with that
> either. So what is everyone else using??
>
>              Thanks
>                        Rick  KA2PBO   
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