Coils for Ion

[Raymond C Drouillard]

On Thu, 04 Jun 1998 09:11:52 -0400 Clare Snyder <snyder at huron.net>
writes:
>garfield at pilgrimhouse.com wrote:
>> 
>> On Thu, 4 Jun 1998 00:14:26 -0400, cosmic.ray at juno.com (Raymond C
>> Drouillard) wrote:
>> 
>> >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.
>> 
>> If this "a lot easier than" is refering to ION measurements, again,
this
>> is NOT at all what is being measured in ION. The current across that
>> plug when it's arcing is NOT, no how, "measured in microamps", it's
>> orders of magnitude bigger. The current we're measuring with ION has
>> NOTHING to do with the spark current. I've said this over and over
now.
>> OVER? We can't be having to go all the way back to ground zero on
this.
>> ION measures ionization current in the plasma that remains AFTER the
>> flamefront, NOT the spark current. That's after BOTH the spark phase,
>> and the flame propagation phase, have PASSED.
>> 
>> I hope that comment above is intentionally comparing apples to
oranges,
>> but somehow I fear it may not be. Say it ain't so.

I humbly go back to my comment about being tired.  Oh well...


>> 
>> >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.

More snipp
 
>SNIPPPP
>
>Just a minute, guys. I'm no EE, but what has AC impedence got to do with
>a straight DC current measurement? By the time we are measuring this
>Ionization current, all we have running through this coil secondary is
>straight, flatline DC. No? This flat-line DC doesn't give a hoot what
>the impedence in Henries is as long as IT is not attempting to change at
>any great speed. I think we've got a bit of a red herring in the nets.
>
>Just my two Ngwe's worth

Two points:

1) The ionization (and hence the current) will be available only briefly.
 We're not talking about a sinusoidal signal or anything like that, but
the fact that the signal is changing gives it an AC component.  My
origional concern was that the big whopping inductance of the secondary
would not allow that change to be seen on the other side of the coil. 
That concern turned out to be largely unfounded because the inductive
reactance of the coil is small compared to the impedance (resistance) of
the spark gap.

2) Often, someone speaking of a nonlinear resistance will use the term
"impedance".  This may not be exactly correct, but it keeps the listener
from making the assumption that a standard linear resistance is being
discussed.  To be truthful, I don't know if the ionization resistance of
the spark gap is linear.

Ray Drouillard

P.S.
We don't need to insult each other.  This point is tossed out in general,
and is not directed at Clare.

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