An injector, just like a relay or other magnetic circuit with moving parts,
exhibits a kind positive feedback which means it doesn't slowly move into
position but past some threshold it will snap into it's final position.
The force acting on the injector armature is proportional to the current in
the solenoid, and inversely proportional to the square of the distance
between the solenoid pole piece and the armature, i.e. the closer to fully
open the injector is, the stronger the opening force.

Think about bringing one magnetic close to another one, as soon as the
loose magnet starts to move they snap together.

Mike

On 16 December 2015 at 16:53, Neil <picdude3@narwani.org> wrote:

> Correct, but I'm surprised that it took that long.  In some ways I
> should understand, as this is almost the bare minimum current that would
> make it open (lowest I saw that would open it was ~1.4A, but I did not
> scope that), but I would've expected to see some movement, even if just
> a budge, starting earlier.  Just surprising, or enlightening, I guess.
>
> Cheers,
> -Neil.
>
>
>
>
> On 12/15/2015 7:42 PM, Dwayne Reid wrote:
> > Hi there, Neil.
> >
> > I don't find that behavior odd at all.  The injector armature has
> > some mass, which takes time to get moving.
> >
> > dwayne
> >
> >
> > At 10:55 AM 12/15/2015, Neil wrote:
> >> On a side note, I tried using a peak-and-hold injector as a regular
> >> high-impedance injector, with a 5.5-ohm series resistor to limit the m=
ax
> >> current, similar to what some automotive ECU's do.  This behaviour was
> >> interesting.  Note that the max current is developed in 2 ms, but then
> >> the injector does not begin to open until at least another couple ms
> >> later.  I just find this odd.  The current here is measured across a
> >> 0.05-ohm sense resistor between the MOSFET source and ground.
> >> http://tinyurl.com/za44qlz
> >
>
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