Re: acmi error found? - Test Equipment!?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <paul-at-abelian.demon.co.uk>

Terry,

You're certainly getting a good match on Lp - how about mutual
inductance? Surprising how much effect removing the ground foil had
on Lp, +0.6%. The accuracy on flat primaries may in general not be
quite as good as your latest measurements suggest - the high number of
primary turns in use will help to disguise the limits of current
filament summing.

Terry wrote:

> I should note that my secondary has always measured 75.4mH but
> programs seem to like it to be ~1% higher. I wonder if the high
> loss Sonotube is responsible. 

Yes. Slide another sonotube inside your secondary and see if self
inductance changes. 

>  I sure would be handy if it could input inches for the colonies! 

OK. You want USA, British, or Canadian inches? I've assumed USA and
uploaded a version 0.1k which accepts a statement like

 units inches
or
 units metres

Default is metric. This statement should be placed before any coil
definition clauses in the input file, ie near the top!

> I would ask that these issues be included as a errata in the
> program's documentation so 50 years from now someone will not take
> real measurements again and go through all these problems all over
> again (like we do today :-)).

Good idea. A lot of useful and some essential tips on measurement have
passed through this thread. Someone should be collecting these for use
on a 'precision measurements' web page. 

> I guess it should be tested against conical primaries and solenoidal
> primaries too to be sure that basically works but I don't have any
> primaries like that.

True. That sounds suspiciously like another 'call for measurements'.

> This shows what a fine computer modeling program can do!

It shows what simple current filament summing can do, and it looks
like the approach is adequate for practical design work, at least for
flat primaries. acmi was put together by cutting and pasting in the
relevant bits of tssp simulator code. The full simulation delivers
the coupling at HF since it models the distributed mutual coupling to
the precision secondary model. Further modeling work will soon reveal
how well the low frequency k as calculated by acmi applies at HF.

BTW,
If I use the simulator to model coupling at 34kHz with the secondary
loaded by the series combination of 10K ohms and 0.1uF, I get an
apparent Lp at position 0 of 215.8 uH, a fall of 2.6% from the low
frequency value.  This model assumes base of secondary is connected to
the ground plane, which will make a difference as yours was floating I
believe.

Cheers,
--
Paul Nicholson,
Manchester, UK.
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