Help on improving injector control at high freqs

[owner-diy_efi]

Hi

I'm new around here and have tried to "catch up" on things by reading
the archives but haven't really found answers to questions I have
concerning 2 different projects I'm working on.  I'd appreciate
any suggestions.

Right now my question is how I can get more accurate control at high
frequencies.  I'm using an injector to inject various liquids and gases
at high frequencies.  It had been necessary to cycle at about 300Hz.  I
hope to reduce that by an order of magnitude but don't know if that's
going to work. 

The injectors used are (mostly) peak and hold - 1 injector is used in each test
the frequecies were 300 Hz - I hope to drop to about 35 Hz
the total test time is only about 5 seconds
the injector (differential) pressure has been anything from 35psi to 100+psi
the control circuit I made is:
	triggered by a filtered input signal- a sine wave
	the delay from triggering signal and also the injector duty cycle has 
		been manually controlled using a 4098B
	the injector activation was with a MOSFET 2N6766 and a 1N5811 diode
	the usual other parts to adjust and cleanup
	Activation voltage is about 13V (I tried up to 28)
I haven't limited the current to the injector.  I felt there was no need
due to the very short test times and I thought it may lower the upper frequency
limit.

Initially I thought that it would be the activation time that limited the
frequency/control of the injector but now I'm wondering if I could get
more accurate shutoff if I did a peak and hold on the current. In the archives
there were refs to a chip that would do the current limitations.  Would
doing so help injector accuracy at high freqs?  Would just limiting the
current with a resistor help.  (I'd just give it a try but don't have
the ability right now.  Can someone please suggest a way to get more 
accurate control of the on-off of the injector?  In the long term, the 
next step would be for the amplitude of the activating sine wave signal to 
control the injector duty cycle.  After that, for active control minimizing 
the activating sine wave by adjusting both the delay and the duty cycle.  
For now I need a quick fix on the manual control ciruit.

Thanks

cat

nasa at suns.chinalake.navy.mil