Coils for Ion

[Raymond C Drouillard]

>See, with that lil tidbit he shared with me, and I simply pass along to
>you, you are now prepared to explain EVERY single feature of the HV IGN
>trace on a scope, should you ever be asked to do so at a cocktail party
>or beer bust. The peaks, the ringing, the arc line, all make perfect
>sense; and now the fuzz on the arc line does too!  B)
>
>Gar

Garfield,

Thanks for the info.  I hadn't even given a though to the arc line.  I
wonder if that line thickens when there is a knock.  I should get with my
mechanic friend and test this out.  A capaciter to pick off the arc noise
is a lot easier than a HV diode to read a current measured in microamps.

Trivia:  The earliest radio transmitters consisted of a spark gap and an
antenna.  Later, they refined it with a tank (parellel LC circuit) in
parellel with the arc so that they could actually tune the thing.

Anyhow, after sending my reply last night, I did do some thinking about
the subject.  I decided that I was barking up the wrong tree on some of
it.  Instead of looking at the sensor resistance, I decided to calculate
the impedance of the spark gap.  Based on your statement that the current
is around a microamp, and the voltage is 80 or 400, the impedance of the
gap is in the neighborhood of 80-400 meg ohms.  Of course, it's this
impedance that we are, in effect, measuring.  While at work (I don't have
access to the web at home, except for email), I looked at some of the
URLs that I got off this list and found some secondary inductances quoted
at 40 Hy or so.  Taking the worst case (80 meg ohm and 50 Hy), I get a
3db frequency of around 150 KHz.  That sounds kinda high... I think I'll
double-check my math later when I'm less tired.

Anyhow, I wasn't considering the ringing because I figured it would have
to decay before we can get a good reading, anyhow.  Also, I believe that
the ringing is due to the primary and the condenser (as in points, plugs,
condenser) forming a parellel LC circuit.


Cheers,
Ray Drouillard, KA8UUU

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