[Diy_efi] Measuring Pulse Width/Duty Cycle of an Injector?

[Daniel R. Nicoson]

To measure the pulse width of both a hi impedance and lo impedance (P&H)
injector I would take the signal between the injector and the computer's
transistor.  Use a comparator to create a nice clean square wave to measure.

For a hi impedance injector you will see the voltage go from 12-14 volts
down to 0 - .6 volts as the injector opens.  The voltage will stay there
until the PW is over going back up.

For the low impedance, you will see the voltage drop as described above and
then go back up to 8 volts or so for the hold portion.

I would use a comparator to create your square wave.  Set the reference so
the comparator trips around 10 volts, this will ensure you can then measure
both hi & low impedance injector pulswidths.

Go to Digi-Key.com and download the data sheet for a LM398.  This is a
sample & hold chip.  I used two in series to create a very nice steady
output on my project.  The data sheet will have example circuits to help you
figure the rest of the circuit out.  You will also need negative voltage
supply for use with this chip, I used the ICL7660.

The 8 & 10 volts mentioned above are approximate.  You may find starting
voltages approaching these values (hope not) and that may or may not be a
problem for you.

Also, be aware of the inductive spike as the injectors close or the P & H
goes from Peak to hold.  Your circuit may need some diode therapy to deal
with these.  I used a combination of high resistance on the input from the
injector line and some diodes to keep the spike out of my circuit.

I have a write up on my sequential secondary injection system on my web site
www.myo-p.com  I used three channels of feed back on that circuit.

Have fun.

Dan Nicoson


> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of gary
> Sent: Sunday, May 22, 2005 2:47 PM
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] Measuring Pulse Width/Duty Cycle of an Injector?
>
>
> (P)eak & (H)old.....  low impedance injector
> In reference to post below, the electronic kits and/or assembly
> books for such kits, for injector DC monitoring and to allow
> monitoring of P & H injectors can be can be obtained through
> AutoSpeed and Silicon Chip, both native of your country.
>
> GAS
>
> ----- Original Message -----
> From: "Mike" <niche at iinet.net.au>
> To: <diy_efi at diy-efi.org>
> Sent: Sunday, May 22, 2005 1:29 PM
> Subject: RE: [Diy_efi] Measuring Pulse Width/Duty Cycle of an Injector?
>
>
> > At 08:32 PM 22/05/05, you wrote:
> > I have seen a kit that converts a P&H waveform into an equivalent
> > simple pulse waveform, expressly for the purpose of duty cycle
> > measurement.  It uses a dual op-amp IC and a handful of other small
> > components.  I have a magazine article that
> >
> > Sorry I'm missing something here - whats P & H ?
> > Did u mean Pulse Width ?
> >
> > Regards from
> > Mike Massen
> > Perth, Western Australia
> > VL Commodore Fuse Rail that wont warp or melt !
> > Twin Tyre rims and tyres for sedans
> > http://niche.iinet.net.au
> >
> > > describes it.  Let me know if you need more info, or contact me
> > > off-list if you'd like the name of the kit retailer.
> > >
> > >Cheers
>
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