Knock alarm

[Tony Cooper]

Chris Conlon wrote:
> 
> Tony Cooper wrote:
> >
> > David Piper wrote:
> >
> > > Can someone comment on the availability of a knock sensor alarm.  Which
> > > sensor would have universal applicability?  How could I fab a circuit to
> > > ...
> >
> > You may have a problem here.
> > The sensor sounds about right, but you will have a problem making a

<Small Snip>

> Is there somewhere I can go to learn more details about how knock sensors
> work? It sounds like they use a resonant sensor, chosen & tuned for the
> application, and maybe look for a build-up of oscillation?
> 
> I had this idea to use something like a (non-resonant) quartz transducer,
> maybe one per cylinder, to get a signal when each cylinder fires. Then I
> could monitor the signal under normal conditions, to get a baseline. A
> knock should give a stronger, shorter signal, a bit earlier, right? Even if
> it needed a DSP, and tuning for each engine, it'd still be useful to me.
> 
> I had heard that some aftermarket ignition system had this kind of setup,
> but I can't find any info on any such thing.
> 
>    TIA,
>    Chris Conlon
> 
> p.s. Hi, I'm new :)

Knock sensor technology is not very 'high'... In fact our experiments
have shown that any robust pickup device will do the job. What I mean
is, if you had an industrial microphone, then that would work too - A
few knock sensors are now based around accellerometers, which in the
most basic form are microphones with weights attached to the diaphram to
give bigger signals, but lower frequency responce (Simple view - please
no flames!!!).

A quartz transducer will do the job, as long as it has a frequency
responce of about 50Hz to 7kHz. No need to put one per cylinder, the
engine block is a good transmitter of sound (read ocillation). The DSP
idea is good, we have implemented it in our adaptive system - also it
doesn't need to be tuned for each engine it is used on, it just looks
for large peaks in the frequency spectrum (after learning the baseline
for the engine that is) at certain times through the combustion stroke.
I think I may stop now, as I might be giving to much away!, and my
business partner is watching me...

Tony

P.S. I may go into more detail when he is gone!!!....

-- 
Sent By Tony Cooper.
email: tony.cooper at virgin.net
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