[Diy_efi] About MAP sensing and it's jitter

[Tomas Sokorai Sch.]

On Wednesday 14 January 2004 14:57, steve ravet wrote:
> Alexei Pavlov wrote:
> > alexis.pavlov at st.com wrote:
> > > tsokorai at xperts.cl wrote:
> > > > Right now in my test code, one sample is taken for every cylinder, as
> > > > my timing marks on the crankshaft are 4, 90 deg. apart. That makes 8
> > > > signals every engine cycle (2 crankshaft rotations). Is it a good
> > > > idea to still lowpass filter them?
> >
> > I've looked at the signal charts. I still find signal dirty.
> > The danger with your approach of sampling is to undersample, even
> > if many diy EFI systems seem to do the same way.
>
> There's an article on the gmecm page about how GM implements lag filters
> for O2, MAP, etc.  It's always a good idea to filter based on your
> sample rate.  In the case of MAP you can do it with a small orifice
> restriction in the line to the MAP sensor, or electrically, or in
> software.
>
> --steve

Thanks!, I'm already using a filter like that on the coolant temp. input. But 
it has a fixed filter coefficient (. I guess that to implement such filter on 
a signal with a sampling rate dependant on the engine speed, it could be a 
good idea to lower the coefficient proportionally with the RPM increase?

-- 
Tomas J. Sokorai Sch.
Socio director, Gerente Proyectos Especiales
Xperts Ltda. F: 63 244591, Valdivia, Chile

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