Re: Variable Mutual Inductance Primary Tuning (VMIPT Sorry :o)))

["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>

Terry,

You wrote:
> Space (in)      Fo (kHz)        L(uH) (0.2uF)
> 0.5             480             0.55
> 1               481             0.55
> 2               526             0.46
> 3               551             0.42
> 4               565             0.40

> These measurements probably have a generally high error ;

They look pretty good to me.  Something went a bit funny with
your 1" measurement, I think.  Acmi calculates:

dist|L1 uH|L2 uH| M uH|La uH|Fa kHz|Lb uH|Fb kHz
 0.5|0.689|0.689|0.443|0.566|   473|0.123|  1015
 1.0|0.689|0.689|0.323|0.506|   500|0.183|   832
 1.5|0.689|0.689|0.254|0.471|   518|0.217|   763
 2.0|0.689|0.689|0.208|0.448|   532|0.241|   726
 2.5|0.689|0.689|0.173|0.431|   542|0.258|   701
 3.0|0.689|0.689|0.146|0.418|   551|0.271|   683
 3.5|0.689|0.689|0.125|0.407|   558|0.282|   670
 4.0|0.689|0.689|0.108|0.398|   564|0.291|   660

which agrees to 3% or better except for the 1" reading -
your measurement seems well off the curve there.

La and Fa are the inductance and Fres of the combination in
parallel.  Lb and Fb are for the combination in anti-parallel.

Note how you get a much wider tuning range with the anti-parallel
version - but the differential voltage between corresponding points
of each turn is high in this case, so close separation might be
limited.

> VMIPT

How about IPT - interactive primary tuning.

> ...MandK, realizing that it was never made to do this type of
> stuff

acmi was, here's the input file for the above output.

; ACMI input file for Terry's parallel primary.
; See http://www.abelian.demon.co.uk/acmi/ 

C = 0.2e-6             ; Primary cap value - Farads
d = [from 0.5 to 4 step 0.5]  ; Range of separations - inches

primary1 {
   radius 11.5/2"
   height  0.0
   conductor 3/8/2"  ; wire radius
   turns 1
}
primary2 {
   radius 11.5/2"
   height  d"
   conductor 3/8/2"  ; wire radius
   turns 1
}

show d as "dist" format "3.1"

L1 = self(primary1)
L2 = self(primary2)
show L1*1e6 as "L1 uH" format "5.3"
show L2*1e6 as "L2 uH" format "5.3"

M = mutual(primary1, primary2)
show M*1e6 as "M uH" format "5.3"

; a = parallel, b = anti-parallel
La = (L1*L2-M*M)/(L1+L2-2*M)
Lb = (L1*L2-M*M)/(L1+L2+2*M)

show La*1e6 as "La uH" format "5.3"
show 1/(2*PI*sqrt(La*C))/1000 as "Fa kHz" format "3.0"

show Lb*1e6 as "Lb uH" format "5.3"
show 1/(2*PI*sqrt(Lb*C))/1000 as "Fb kHz" format "3.0"


--
Paul Nicholson
--