Re: BPS measurement, was Re: [TCML] Spark gap

[Chip Atkinson <chip@xxxxxxxxxx>]

This sounds like a model airplane tachometer almost.  Here's a link:
http://www.valuetesters.com/Extech-461825-Photo-Tachometer-Stroboscope.php

I remember tachometers that would just detect the pulses of light as the
propeller would oclude the sensor.  Perhaps this sort of thing would work.

Chip

On Mon, 25 Feb 2008 FIFTYGUY@xxxxxxx wrote:

>  
>  
> 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
> 
> 
> 
> **************Ideas to please picky eaters. Watch video on AOL Living.      
> (http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/
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