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RE: [TCML] Oscilloscope Tuning
Group, Bart & Dr'
With two overexcited, overfed, Xmas visiting grandchildren charging around
the house and narrowly missing my clock collection at times, my thoughts
turned to Tesla's. Think what you want into that........
Using my escape tunnel this morning to the workshop I found that with a 4kz
square wave input I can extend the timebase and get a much better trace
without the noise that I had at 1Khz.
This now clearly shows what I wanted to see. See
http://homepage.ntlworld.com/follies/temp/scope_at_4khz.jpg
I found that a sine wave input (or even a triangular one) does not show the
dampening resonance though, instead the result is much more like a normal
charge/discharge curve.
With Antonio's tuning method he recommends a 1 ohm resistor across the SG,
but I have found this is not too critical, although it does need some low R.
Must go back now before the tunnel entrance is discovered.
Phil
-----Original Message-----
From: bartb [mailto:bartb@xxxxxxxxxxxxxxxx]
Sent: 24 December 2008 23:51
To: Tesla Coil Mailing List
Subject: Re: [TCML] Oscilloscope Tuning
Hi Phil,
Good job with tuning procedures. I personally have not performed
Antonio's tuning method. I really liked the fact that you looked at
streamer loading (it is significant). Note, programs today are not
looking at streamer loading. Thus, as you can imagine, coils are built
to spec, but when streamer loading comes into play (or other external
C), an extra primary turn or so comes in handy (on some coils more than
others). For your coil, to tune to this streamer load, you would need to
increase L1 a little. This is completely normal.
Someday, we will accommodate streamers loads at least to a common
streamer load factor as based on predicted spark length.
Your pic showed 2.4 divisions at 0.2ms? So, 2.083kHz. You should be able
to set the time base on the scope to spread out the "rise and ring
down". It doesn't take a modern scope to do this kind of measurement.
Almost anything will do fine.
Take care,
Bart
Phil Tuck wrote:
> Hello.
>
> I have just tried a method of tuning the coil using a 'scope and signal
> genny, that was suggested in the archives by Antonio Carlos M. de Queiroz
.
>
> I had already tuned it in the 'normal' fashion of injecting a signal in
the
> base of the secondary and hanging the probe close by. The secondary &
toroid
> were mounted in their usual place but the SG was left open circuit to
> avoid the primary LC affecting things. I also tried it with the
> secondary/toroid well away from the primary just to 'be safe' and the
result
> looked on the scope to be the same.
>
> I do not have a frequency counter so I get the resonant peak on the
scope,
> and then connect the scope across the signal genny to get a truer result
of
> the frequency rather than reading the [rather course] dial. So small
> differences won't show as the scope's 'eyeball' resolution is limited to
> around 0.1 divisions.
>
> I had also hung a piece of wire to the toroid to simulate a streamer.
[The
> difference between simulating a streamer and without one a drop of around
> 18kHz - 156.25 down to 138.88 kHz a drop of 11.1%]
>
>
>
> The primary was then checked with the SG shorted and the genny and 'scope
> across the inductor/caps. The secondary was removed completely for this
part
> though. After some adjustments to the tap point, both resonant
frequencies
> were the same [secondary with a simulated streamer].
>
>
>
> I then tried Antonio's method of placing a 1.5 ohm resistor across the gap
> and connecting the signal genny in parallel to it running at 1Khz square
> wave output. The secondary and top load were connected and back in place,
> whilst the NST and Terry were disconnected. The scope was placed across
the
> primary coil.
>
>
>
> The resultant trace can be seen here:
> http://homepage.ntlworld.com/follies/temp/scope.jpg
>
>
>
> It looks like it may be correct as I can see what I presume to be the
> ringdown, but I remember seeing a scope trace somewhere else on the web
> where the abrupt sharp Y axis rises that I have, were replaced with more
> gradual 'ringup' shapes, so I wondered what anyone else on here thought.
>
>
>
> Both my 20 year old scopes are the limiting factor most likely as
decreasing
> the time base makes the trace even more noisy and unreadable.
>
>
>
> As a point of interest the signal genny output was around 15 - 20 volts
and
> the scope timebase is 0.2 millisecond giving what I suppose [bear in mind
> that the primary was running on 15 volts with no spark gap needing to
fire]
> would be an equivalent break rate of around 1/( 2.4 x 0.0002) = 2083 bps.
>
>
>
> Regards
>
> Phil
>
>
>
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>
>
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