RE: Sparks - Bright in the middle, how to verify it - suggestion

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

Original poster: "Dale Hall by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Dale.Hall-at-trw-dot-com>

Suggestion:
While HS filming also synchronously record
arc current with an oscilloscope (Iarc Vfield and Isec) 
if possible in the same frame.

I've used a CT, Current Transformer, with an oscilloscope
(large throat Tektronix probe + current amplifier) 
in the arc return path for capture with my batt powered 
manually triggered SS DC TC to photograph power arcs from 
0 to ~22" -at-2.45J/bang (could do 38" now -at-4.9J) and compare to 
DSO waveforms.
a couple are at 2.45J:
http://www.cowmail-dot-net/dalehalldctc/

4.9J (just arc photos)
http://hot-streamer-dot-com/TeslaCoils/Temp/
see: 09bal..., 12bal..., 15bal...

The electrical characterization when compared to the optical 
reveals what is going on, midstream or either end of an arc.

It would be wonderful to capture these synchronously 
representing the evidence of same single arc event.
to observe the time correlation from gap firing = scope trigger,
electrical waveform activity presentation on the oscilloscope, 
of power arc discharge inception to termination 
and all the intervening 'characterization'
representing various arc tree paths, 
the dead end branches as well as the main power path
and likely explain the 'bright' arc areas.

This is something I've been wanting to do for a long time.
A manually controlled single shot DC TC I would think is be ideal
so cause and effect would be so much easier to realize.

I have hundreds of 1 Mpixel digital camera power arc photos.
About half show intensity differential: beginning, end or middle.

Regards, Dale
Redondo Beach, Calif

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, January 21, 2001 8:16 AM
To: tesla-at-pupman-dot-com
Subject: Re: Sparks - Bright in the middle, how to verify it.


Original poster: "Mike Harrison by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <mike-at-whitewing.co.uk>

On Sat, 20 Jan 2001 11:33:06 -0700, you wrote:

>Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>
>
>The same phenomenon, in a slightly different form, is also evident on Van
>deGraaf generators.  Sparks tend to grow from one polarity better than the
>other.  When you run your coil on AC, the polarity of the top is reversed
>every half cycle.  On one half cycle, the spark is growing from the ground
>rod towards the terminal, on the other half cycle, it is the opposite.  If
>your spark length is 2/3 the length of the gap between the terminals, in the
>middle third, you'll see twice the brightness.
>
>I'd love for someone who has a very fast video camera (one of those 1000
>frames/second jobs) to take a look at TC sparks.  When I worked in the movie
>business, we used to do shoots where for super slow-mo they used to run
>cameras at 300 fps or faster (thousands of frames/second), but I couldn't
>ever work a deal where they'd film my little coil as an experiment.  There
>was always a schedule conflict, or I didn't have the cash for the film and
>processing. At $1/foot, 300 frames (around 25 feet) costs about $25, so
>burning a minute of film is a pretty pricey experiment.  Production
>companies may be profligate with star salaries and cushy seats for the
>advertising agency guys, but they're pretty stingy with the below the line
>costs like film, processing, and staff.
>
>However, there are a lot of the new Kodak and NAC motion analysis systems
>with very fast CCD cameras hooked to a computer around now and the rental
>prices are coming down.  Maybe next time there is a "teslathon" in the area,
>I will rent one.
>
>You might also be able to improvise something using the fast shutter mode on
>consumer video gear.  It has a shutter speed of 1/10,000 second (or so), but
>the frame rate is going to be 60 Hz.  You might get useful data if you could
>slowly vary the phasing of the power driving the coil relative to that in
>the camera (actually, the camera probably isn't that stable, so it would
>drift by itself). You're not going to get the ideal, a series of frames on
>the same spark, but, you might get a feel for spark growth in general, as a
>function of time past "bang".

I thought of doing this a while ago as I have a camera with an
external sync input, which could be locked from a mains derived source
with an adjustable delay. The problem, however, with both film and
video methods is sensitivity, or lack of it. When you take a video
camera down to 1/10,000 sec, you need an awful lot of light, and would
need to look at pretty big sparks to get a useable picture.  This is
not helped by the fact that as sparks are a 3-d phenomenon, you need a
reasonable depth-of-field, and so you may also need to reduce the
aperture to get a sharp picture.

One possibility I did think of, is that webcam type devices are
getting very cheap nowadays, so it might be feasible to use several of
these to take a small sequence of pics in rapid succession with
appropriate syncing. 3-d spark pics would also be possible with such
an array. A bunch  of disposable film cameras could also be a
possibility.....

I've also frequently noticed the 'bright centre' phenomenon on several
coils. I also saw the opposite effect, a dark centre, when playing
with a piezo gas lighter recently. 
 
>A DC coil running off a well filtered supply might also be easier to
>synchronize to
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Saturday, January 20, 2001 8:36 AM
>Subject: Re: Sparks
>
>
>> Original poster: "Charles Hobson by way of Terry Fritz
><twftesla-at-uswest-dot-net>" <charles.a.hobson-at-btinternet-dot-com>
>>
>> Hello all,
>>
>> Placing a grounded rod about 300mm from the terminal of my coil I get nice
>> sparks similar in appearance to lightning. At the center of these sparks
>> there is a 25mm segment which is much brighter than the rest. I would be
>> most grateful for an explanation for this phenomena.
>>
>> Chuck
>>
>>
>>
>>
>
>
>