# Re: Mutual Inductance and Coupling Measurement

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From: 	DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: 	Saturday, August 09, 1997 5:03 PM
To: 	Tesla List
Subject: 	Re: Mutual Inductance and Coupling Measurement

To: Greg

Perhaps trying the same experiment with an older vacuum tube signal
generator (vac. tube provides more drive potential) with a 2 v. drive.
Then repeat the same experiment on the same coil with your 120 v method and
compare the results.  We have always use the sig. generator method but will
try the 120 v method on a coil next week to see if there is any difference.

DR.RESONANCE-at-next-wave-dot-net

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> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Mutual Inductance and Coupling Measurement
> Date: Saturday,August 09,1997 11:59 AM
>
>
> From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
> Sent: 	Saturday, August 09, 1997 12:51 PM
> To: 	Tesla List
> Subject: 	Re: Mutual Inductance and Coupling Measurement
>
> Edward V. Phillips wrote:
>
>
> >         Here is a pretty fundamental way to measure the mutual
> > inductance, provided you have a millivoltmeter.  Feed a known
> > 60 cycle current (say power line in series with 100 watt light
> > bulb) through one winding and measure the induced voltage
> > across the other.  Suppose, for instance, that the mutual
> > inductance is 100 microhenries.  This represents a reactance
> > of 0.0377 ohms at power line frequency, so the voltage will
> > be omega x M x I = 377 x 100 E-6 x 1 =37.7 millivolts.
> >         Having measured M the coupling factor k is the
> > mutual inductance M divided by the square root of L1 x L2,
> > where L1 and L2 are the winding inductances.
> > Ed
>
>
> Your method is also my favorite way for measuring M and k,
> since all you need is a Fluke 77 and a 120V 'suicide cord'!
> I connect the 120VAC directly across the secondary, however,
> in order to get maximum primary signal level.  The induced
> primary voltage usually falls in the 0.20V to 0.40V range. A
> calibration chart placed near the coupling adjustment cranks
> makes it easier to dial in the coupling.
>
> This is also a great way to measure the secondary self inductance,
> as the drive freq is very well defined. And since the current in the
> secondary is only 6.15A at 120VAC, ohmic heating is not an issue.
>
> I wonder though if the coupling between the pri and sec at 60Hz is
> the same as at 60kHz?  Could the reactive currents in the secondary
> at resonance shape the magnetic field in a different way?
>
>
> -GL
>
>

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