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Re: Variation of secondary Q



Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Paul,

At 04:34 PM 3/19/2002 +0000, you wrote:
>Terry wrote:
>...
>> Instead of using the signal generator that only does a tiny 20
>> volt P-P, why not just charge the sucker up to 1000 volts and
>> let an IGBT short it to ground.
>
>Yes, if you want to, it will mean you can move the field pickup
>further away.  As you'll see below, the data you supplied in
>TEK00001.CSV for the single shot is more than adequate.

Hopefully I could then use the Pearson current monitor.  That would be far
more better signal wise.

>
>The carrier at 227.4 kHz +/- 75 Hz is nothing to do with the coil,
>have you a strong broadcast station at that frequency nearby?

My long wave radio could not pick up anything at all near this.  Maybe one
of the neighbors was running a Tesla coil :o)

>...

>ringdown highlighted in green in 
>
> http://www.abelian.demon.co.uk/tmp/tek00001.croptd.gif 
>
>The next step is to match a synthesised waveform of the form
>
>  A * cos( 2*pi*Fres*t) * exp( -r*t)
>
>to the cleaned up signal.  We already know the complex number A
>from the FT, so we only have a to do a least squares match over the
>the exponent r, and from this, Q = pi * Fres/r.  For this sample
>I get roughly 219.6 +/- 2.  

Neat!  That's is right near what I was getting with the old setup.  So it
all basically works.

>In order to get the full accuracy on Q
>we'll need to subject the above synthesised waveform to the same FT
>band limiting as the trace signal is processed through, so that
>they have compatible envelopes (the band limiting means the decay
>is no longer quite exponential).
>
>Was the single shot TEK00001.CSV a top-volts (direct probe) or an
>E-field pickup, a base current pickup, or a B field pickup?  Try to
>avoid any probes near or on the coil. 

It was a very near E-field pickup.  But I think with high voltage, the
current monitor's signal would do fine.  I could then fire the coil with
all remote stuff and only a long terminated coax would be needed back to
the scope.

>
>> I have been looking at the "NEW!!" Tektronix TDS3GV plug in to
>> enable RS-232.

I was looking at this today and the programming part and it looks like the
way to go.  WaveStar may do it by itself but just programming it in BASIC
looks pretty easy.  I note this PowerPC based scope has a bazaar number of
commands...  Maybe time to upgrade to the latest firmware version (a
freebie) too...

>
>Might be worth trying the soundcard capture first, as a cheap and
>cheerful option.  If that could be made to work (quite likely I 
>think) then this trace analysis method could be used by many more
>people.  With your sig gen set to 75kHz, a diode and an RC or two
>should give you a noisy 10kHz ringdown waveform at the soundcard
>input.

None of my cheap computers have sound.  Just getting the RS-232 interface
seems the best ways to go and adds yet another toy to my collection. :-))
Still trying to find a reason to by the 34970a data logger ;o))  I'll try
to do some HV testing tonight and if all looks good I'll see about getting
the interface.  I can always sell it on ebay for more than the new price
:o))  Interesting how the new scopes are impossible to find used...  Not
even parts...

>
>I'll tidy up the code and send it to you.  You'll have to compile
>and run it on the Sun - I haven't a Green-haired Turtle in Taiwan's
>chance of getting this to run on windoze (yuck, spit).


Cheers,

	Terry

>--
>Paul Nicholson
>--
>