Re: [TCML] predicting phase shift

[bartb <bartb@xxxxxxxxxxxxxxxx>]

he.. yes, your correct (frequency changes inductance).

I knew I should have gone to bed early tonight! :-)

Later,
Bart

piranha wrote:
> Odd...  The inductance of a secondary coil measured with a 1kHz hand 
> very low current held meter matches the coil's inductance at many amps 
> and 100's of kV during operation... :)
>
> For an air core inductor without saturation effects, the inductance 
> value is pretty darn stable ;)  Independent of current and voltage 
> unless you melt it or arc it over.  In high impedance circuits, 
> Medhurst effects are seen but the inductance still stays the same.  
> There are also some transmission line effects but those are also 
> independent of current.  There is also series resistance but, that is 
> still independent of current.  Current distribution in the wire along 
> with relativistic effects are also independent of current.
>
> Inductance can change with frequency.  If you measure a coil at say 
> 100GHz you will get some odd readings.  But in our case at say 100kHz, 
> you just don't have to worry about it.
>
> If you see the inductance of your secondary inductor seems to be 
> varying a lot, you left the base ground wire off :D
>
> Terry
>
>
> bartb wrote:
> > Wow, hate to even get involved in this thread, but...
> >
> > Sure, inductance will vary with the rate at which the current is 
> > changing in the inductor (it has to). Phenomenon like current 
> > bunching in a coil, long solenoid coils at high frequency, etc. will 
> > have a different inductance in one portion of the coil as compared to 
> > another. The lumped average over the entire coil would be the 
> > effective inductance which the coil will use for it's LC resonance. 
> > Hard to measure things like that however and they are best viewed 
> > with software. Software predicts this also. We've all heard of high 
> > frequency inductances and capacitances.. This is simply "that".
> >
> > However, I have no clue what that has to do with Hammers circuit. The 
> > bottom line is that the coil will have an inductance at some 
> > frequency. Although it will vary from say a low frequency inductance, 
> > it will not change enough at the resonant frequency to make any 
> > difference. The IGBT's have a "known" delay, and the circuit is a 
> > simple way to provide a consistent zero crossing prediction.
> >
> > Bart B. Anderson
> > Modesto, CA USA
> >
> > Lau, Gary wrote:
> > > Inductance changes as the current through it changes?  I don't think 
> > > I've ever heard that before.  As most inductors are used in AC 
> > > circuits and the currents are constantly changing, that would be 
> > > basically all inductor all the time.  Please clarify?
> > >
> > > Gary Lau
> > > MA, USA
> > >  
> > > > Any time the current is changing dynamically the inductance also 
> > > > changes
> > > > --- it pure physics and basic E.E., not smoke and mirrors.
> > > >
> > > > D.C. Cox
> > > >     
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