TSSP: List Archives

From: Paul
Date: Thu, 15 Feb 2001 18:55:19 +0000
Subject: Re: [TSSP] Top voltage testing

Terry wrote:

> Winding length = 26.125 inches
> Diameter = 4.25
> #24 wire = 0.0201 diameter
> Turns = 1180?
> Rdc = 34.0
> Ldc = 22.1mH
> Height off ground plane = 0.35 inches

Putting these dimensions into the model gives

       measured      modeled     error
Rdc:   34.0 ohms     34.2 ohms   +0.6%
Ldc:   22.1 mH       22.54 mH    +2.0%

(I used the measured Ldc, rather than the calculated, in what follows.
Are we seeing reduced Ldc due to eddy current coupling to the foil?)

f1:   358.3 kHz     357.3 kHz    -0.3%

> Using the Tek 5100 probe on the top I get:
> F1 = 311.3kHz
> Iin = 0.20815mA
> Vtop = 7.9465V
>
> I calculate that the H/D is 6.1471
> Vtop / Iin = 38168 ohms
> Zes = 19.5135mH or 88.3% of Ldc

OK, I find that 3.11 pF of probe capacitance is necessary to reproduce
this f1:

       measured      modeled     error
f1:   311.3 kHz     311.3 kHz     0.0%   Ctop adjusted to match
Zft:  38168 ohms    34903 ohms   -8.6%
Les:  19.5135 mH    17.8 mH      -8.6%

Roughly speaking, the model predicts Les at 80% of Ldc, and you're
splitting the difference at 88% Ldc,

Can you check that you have an f3 lurking at around 871 kHz for the bare
coil and 829 kHz in the probed coil.

How come the base current dropped so much between the bare and probed
readings?

Cheers,
--
Paul Nicholson,
Manchester, UK.
--


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.