RE: Dimensions of my flat spiral coil

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

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Jim,

>Does the spec sheet give any data on whether that is a 2 sigma uncertainty
(often the case when not otherwise specified...  if error is gaussian, then
it's roughly a 95% confidence interval)?

Not that I can see.  Where can I quickly learn about sigma and epsilon?
I've been seeing these terms a lot lately and I have no clue what they mean.

>Naahhh.. the difference in length is so small, compared to the overall
coil. You have hundreds of turns.  A third turn isn't going to make all that
much difference. A bounding case would have L proportional to N^2 (and in
reality, the exponent is lower).  So, if you have 400 turns, adding a whole
turn is only going to change the inductance by (400/401)^2.. about 0.5%,
which is a lot lower than your measurement uncertainty.

I'll take your word on this for now.  But on my next wye coil, I'm going to
measure the inductance of each strand while the leads are together and then
measure them spread 120 degrees.  I need the certainty of direct experience
to fully accept this idea.

>... you can deliberately perturb the surroundings, and see how much of a
difference it makes.  For instance, if you put a steel plate 2 feet away,
and repeat the measurement, and it doesn't vary more than the measurement
uncertainty, then you can kind of figure that you're insensitive to
disturbances of that type.

Great advice.  I'll do this with my next measurements.

Dave