acmi accuracy...

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Paul,

At 11:22 AM 12/23/2000 +0000, you wrote:
>
>Thanks to measurements from Bert, Bart, and Terry, I've been able to 
>make some improvements to acmi. It no longer rounds to integer turns,
>it handles fractional turns to a resolution of 1/10th turn. It also
>approximates better the spiral winding, by representing it as a number
>of segments of concentric circles of intermediate radius. Also, I've
>taken the filament radius for larger conductors as being the inner
>radius of the turn. Each of these changes gave an improvement in
>accuracy, and the results are now summarised in
>
>   http://www.abelian.demon.co.uk/tmp/acmi-compare.html
>
>This version 0.1f of acmi is up on the website,
>
>  http://www.abelian.demon.co.uk/acmi/
>
>We still have some trending in k, but the trends from Bart's and
>Terry's readings are opposite. Awaiting further measurements to
>resolve this. Primary self inductance errs consistently on the high
>side. If this persists, I'll put in a calibration factor.
>

I have finally gotten the program and have used it.  Very nice!  Many
thanks for the DOS version for us non-UNIX folks 0:-)

I see that the error seems to increase when the primary and secondary are
aligned at the base or when the coupling is greatest.  I think there are
six possible causes for this:

1.	Floor too close - In my measurements, the primary was only 4 inches off
the concrete floor.  Perhaps this is causing the error.

2.	Primary to secondary capacitance - Perhaps when the coils are close, the
primary to secondary capacitive effects are a factor.

3.	Winding direction - perhaps related to #2, the winding direction may
tend to add or subtract from the coupling.  This may explain why Bart and
my measurements trend in opposite directions.

4.	Measurement error - Perhaps there is something in the technique of
taking the measurement that is causing the error.  Also, the meters I used
at the time were probably 1% accurate.  I now have two true RMS meters.
One 4 digit and the 6 digit HP34401A.  I could probably stretch the
accuracy out by two more digits now.

5.	The program - Coding causing the error but the measurements are fine...

6.	Unused primary turns - I use 15 of 19 turns.  Perhaps the unused turns
are having some auto transformer or capacitive effect.

To check into these I could try the following tests:

1.	Measure the 1000Hz primary to secondary capacitance at the 15 heights.
2.	Raise the coil off the floor by a foot or so and retake the measurements.
3.	Use the better meters and big fixed ceramic resistors for current
limiting to reduce pure measurement error.
4.	I can't think of a way to change winding direction.  If you turn the
secondary upside down it stays the same winding direction.  Turning the
primary over is awkward at best in my case and I don't think I would trust
that.
5.	Try using all the primary turns to eliminate the effects of the unused ones.
6.  	??? Can anyone else think of others or why one of these is not possible??

I have a request:
It would be nice if acmi could input and output the numbers to many more
digits, at least while were trying to split hairs here.  The 0.001
resolution for k seems rather course (wow, aren't we picky :-)).  Also, if
it could do primary turns to the nearest 100th or 1000th, I could put in my
15.125 primary turns without worry.  With higher resolution, some of these
errors would be easier to quantify and "err%" my be much better.  So I
would ask that the outputs have more digits for the time being.  My free C
compiler gave some error (LCC didn't like "strncasecmp") or I would do this
myself.

Cheers,

	Terry