A repost

[Bruce Bowling]

> 
> A slightly more sophisticated curcuit would allow you to alter the 
> duty cycle (via a pot), to allow holding the pintle just off its 
> seat (say vibrate between 0 and 10% open), as opposed to the above 
> circuit that will probably just hold the injector between 90%-100% 
> open.

The pot is a good addition.

I do not think that the above circuit will just keep the injector
open. Most injectors take at least 1 millisecond to open. And
what I have been told is that it takes roughly the same amount
of time to close. The driven frequency of the circuit is 10 khz,
or a period of 0.1 milliseconds, at ~50% duty. So, with a starting condition
of the injector being closed, the injector will open roughly only 10
percent before it closes again. Does the injector take longer to open this
little mount than to close? I do not know, but instinct (only) tells
me that it probably takes a little longer to open the injector than
to close it (open requires overcoming spring force + inertia + charge-up
time of injector solenoid (inductance), whereas closing is inertia +
collapse time of solenoid). I have not thought up of all of the forces
acting on the injector for opening and closing, so I may
be in left field. But 50% duty is a good start, and it works
for me.

But making the duty cycle adjustable is a good addition.

- Bruce


> 
> I suspect the injector will start to scream when you get the duty 
> cycle just right.
> 

It does.


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                 Bruce A. Bowling
                 Staff Scientist
   Thomas Jefferson National Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23606
                 (804) 249-7240
bowling at cebaf.gov  http://devserve.cebaf.gov/~bowling
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