Richard,

  Are you saying that the current into the spark is
too low for the current clamp to detect it?

John

--- Richard Prosser <rhprosser@gmail.com> wrote:

> I've seen inductive coupling used on the primary
> side (ie the wire to
> the points) of the coil for a tacho triggger . On
> the secondary you
> can use  capacitive coupling by wrapping some foil
> around an HT lead
> and adding another capacitor to form a capacitive
> divider & protect
> (somewhat) against the high voltage. You can even
> connect a scope to
> this arrangement to view the waveforms.
> I'm not sure an inductive pickup on the secondary
> side would be too
> effective as the current is pretty low.
> 
> Richard P
> 
> On 26/07/06, Bob Barr <bbarr@california.com> wrote:
> > On Tue, 25 Jul 2006 20:03:01 -0700 (PDT), John
> Chung wrote:
> >
> > >I haven't used a current clamp before so here
> goes.
> > >Can the current clamp detect the rpm of the car?
> Just
> > >hook the clamp to the spark plug line and use the
> Hz
> > >to determine the RPM? Is the clamp sensitive
> enough?
> > >
> >
> > You wouldn't ordinarily use a clamp-on current
> meter for RPM
> > measurements. I don't know if that would even be
> possible.
> >
> > Many automotive timing strobes use a clamp-on
> inductive pickup to
> > trigger the flash circuit when one particular
> sparkplug fires. A
> > timing mark on the crankshaft is used to set the
> ignition timing.
> >
> > Most tachometers, though, connect across the
> points and calculate the
> > RPM from the frequency of the points opening and
> closing.
> >
> >
> > Regards, Bob
> >
> > --
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