Re: Barts Flat Coil Dimensions Was: Dimensions of my flat spiral coil

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

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

Further to previous message, 

I made a little error when estimating the error. Don't know where
the 6.1 came from :)

Measured was 6.23, acmi was 6.31, so acmi is
(6.31 - 6.23)/6.23 = +1.3% wrt the measurement.

Dave, if you want to investigate the residue, then you'll
have to move to a different way of measuring L.  The problem
with the LCR meter is that it's frequency of operation is
too high (circa 1kHz?) for any better accuracy than this, with
large, closewound coils, at least.  The trouble is, the coil's
self-capacitance bypasses a little of the inductance you are
measuring. The meter thus sees a slightly lower reactance than
it would otherwise do, and so delivers a slightly lower inductance
reading.

To reduce this effect, you must work at a lower frequency, eg 60Hz.
Pass a 60Hz current through the windings and carefully measure the
voltage and current.  From these measurements, calculate L.

A second advantage of this approach is that you can also measure
mutual inductances between different windings.  Great care is needed
to achieve accuracy - you would need to use properly calibrated 
instruments, and you must make allowance for the coil's resistance
too.
--
Paul Nicholson
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