Re: acmi error found? - Measuring techniques?

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Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-uswest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>


Hi Bert and all,

Well it's rare that I disagree with you Bert ;-)  but I think something
seems wrong in the method you described below:

> Original poster: "Bert Hickman by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>
> 
> Once the primary and secondary LC circuits are significantly coupled to
> each other, it is difficult to independently measure the primary or
> secondary resonant frequencies. The following process permits proper
> measurement and setup for the primary and secondary by preventing their
> interaction as two tuned LC circuits....
> 
> The loaded secondary's resonant frequency should be measured with the
> secondary/topload installed at its intended operating position within
> the primary. However, while measuring the resonant frequenmcy, both the
> inner lead and tap point of the primary should be shorted together and
> tied to ground. This will prevent the primary LC circuit from affecting
> the measurement. The primary is still "there" with respect to capacitive
> coupling to the secondary, but its no longer a tuned circuit. Measuring
> the resonant frequency of the secondary/topload in this fashion will
> measure it's self-resonant frequency (Fo) when in its operational
> environment. Record this value. 

If you short circuit the primary,  it would seem to me that this short
circuit is reflected to a portion of the secondary coil determined by the
coupling coefficient.  In a way you are "shorting-out" the inductance
which is common to both pri and sec.    For this reason I would expect the
secondary to resonate at a higher than normal frequency due to its
coupling with the shorted primary coil.  The higher the coupling the more
the secondary frequency will be shifted above its natural Fres ???

(I thought you could actually use this method to find the K factor ???)

I would agree with leaving the primary winding in place with _ONE END_
grounded,  and all other connections removed.  But, I don't beleive it
should be shorted out ???

This should give an accurate Fo value for the secondary below breakout.  I
think Fo drops by 5% or so during breakout though !

Does anyone else have any thoughts on this ???

I Hope everyone had a good Christmas,  and I wish you all the best for the
new year,
						Cheers,

						-Richie,