BPS measurement, was Re: [TCML] Spark gap

[FIFTYGUY@xxxxxxx]

In a message dated 2/25/08 9:48:00 P.M. Eastern Standard Time,  
bartb@xxxxxxxxxxxxxxxx writes:

>Here is my very simple strategy:

>* Hook up fiber cable near first gap to capture the light created  by the 

>spark (where it will always issue).

>* Convert light to DCV at opposite end.

>* Record voltage output over 10 minute  run.


    After my post, I gave it some thought. 
 
    My criteria still are:
 
    *pocket sized
    *battery operated
    *direct display of BPS
    *works with vacuum tube, solid state, as well as  spark gap coils
    *cheap and simple
    
    I'll add:
    *range from 100 to 1000 BPS
    *accuracy of +/- 5%
    
    I thought, as you did, that light from the gap  might be a viable 
measurement point. But it would be difficult to get down near  a gap on a running 
coil, and if you were too far from the gap you'd likely get  interference from 
reflections and the secondary arcs. 
    Besides, that wouldn't work on a vacuum tube or  solid state coil.
 
    I figured the antenna method might be the most  reliable. I drew up a 
very simple input end, which on further research turns out  to be the standard AM 
detector circuit (no surprise!). This should turn the  decaying sinusoid 
output into a pulse train. 
    From there, I figured one could run it directly  into a digital 
tachometer panel meter. But those things go for $50+ new, and I  don't have a spare 
sitting around. I looked at the digital photo tachs the model  airplane hobbyists 
use for tuning engines. They run around $20. Maybe it would  be easy to hack 
one (and even use for the basic project box!). Heck, they might  even work 
as-is if you just point it at the gap.
    Or you could run the pulse train into a  Freq-to-voltage converter chip, 
and drive an analog meter (but tough to keep 5%  accuracy at the low end of 
the scale. Maybe not so important, as the 10x range  would be handy enough?
    Or run the pulse train through the usual  manipulations, and drive a 
3-digit LED 7-segment display. Still cheap and  simple, but tedious for me. I'm 
sure there's somebody here who would get some  satisfaction from designing the 
simplest way to implement this. I was hoping Mr.  Piranha would, since this 
would be right up his alley, and "Terry Tach" has a  nice ring to it. ;)
    
    Wouldn't it be great to pull out a little gizmo at  a Teslathon, and 
start comparing each other's breakrates? Yeah, it doesn't get  geekier than that, 
but it would probably reveal a lot and allow for meaningful  discussion 
without the usual speculation and hand-waving.
 
-Phil LaBudde
(yes, I own several oscilloscopes, but I'm lazy)

Center for the Advanced Study of Ballistic  Improbabilities



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