Re: New formula for secondary resonant frequency

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

Original poster: "Kurt Schraner by way of Terry Fritz <twftesla-at-uswest-dot-net>" <k.schraner-at-datacomm.ch>

Hello John,

With x=H/D, im using my own precision-fit formula (avg.deviation
0.27%; max. 1.05%) to the Medhurst K-value table, which was used
by Bert Pool, in his Excel-design sheet, for 1 < H/D < 8. The
function, due to its relatively few parameters etc., behaves
plausibly for slight extrapolation of H/D > 8 (tried up to 10).

Eqn	K=a+b*x+c*x^(1.5)+d*ln(x)/x+e/x^2

a	3.174612104
b	-0.350587741
c	0.087994211
d	-4.628698069
e	-2.451606171

Then Co[pF] = K*D[cm]

I'm aware however, Medhurst himself proposed a formula:

K= 0.1126*x + 0.08 + 0.27/sqrt(x)

...with Co[pF] = K*D[cm]

which he claims to fit his 5% precise data, for 0.163 < H/D <
29.2, closely (to 2..3% --> I'm getting 4.8% avg. and 7.7%max.
error for H/D=1...8). But I've seen, my own fit is introducing
less error in addition to his 5% table, for the range of 1 < H/D
< 8 mostly used for TC's. 

Greets
Kurt Schraner


Tesla list wrote:
> 
> Original poster: "John H. Couture by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>
> 
> Kurt -
> 
> What are you using for the Medhurst equation?
> 
> John Couture
> 
<snip>