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Subject: Re: Automotive EMI
Date: Wed, 25 Sep 2002 10:22:28 +0100
Organization: Kijoma Solutions Ltd
NNTP-Posting-Date: 25 Sep 2002 09:25:13 GMT
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
you could always post proccess after the ADC with averaging in software to
"slow" down the response.
a software "window comparator" may be another solution too.
saves the extra analogue stuff.
Kijoma Solutions Ltd
RF - Analogue - Digital - Software
Electronic Product Design & Consultancy
Email : news@kiSPjoAMma.com ( remove the spam)
There are only 10 types of the people in the world
those who understand binary and those who don't
"Chris Matthaei" wrote in message
Tom Faloon wrote:
> First you need to establish how the noise is getting onto the amplifier.
> The ignition is certainly a possible source, but so is the car electrics.
> You can expect a very 'dirty' supply on automobile electrics. (HF noise
> very large amplitude spikes.)
> **** Other points ****
> What exactly did you mean by 'when the load on the engine increases'
> Are the sensors connected to ground at the point where they are physically
> i.e. could they form earth loops.
> Does the amplifier have a solid earth.
> Is the amplifier in a screened box. (Not suggesting that is essential,
> wondering about the construction.)
> Why 10 Hz cutoff. What decides that?
> ( The lower the better.)
> Tom Faloon
> EMI / EMC
First, thanks to all who responded. What I meant by "load on the engine" is
basically the throttle position. As I approach full throttle, the noise gets
worse. The signal is actually pretty clean at idle and part throttle. It's
when the spark voltage has to overcome a significant fuel-air charge that I
really see the noise. At least that's what I'm guessing is happening. The
sensor I'm attempting to monitor is the Mass Air Flow sensor. I figured 10Hz
would be adequate for this signal since the fastest I'd expect it to change
around 1/10th of a second. I don't have any amplifier at all yet. I have the
MAF signal connected directly to the A/D input.
From the responses I got, I think I'm going to try to make a passive filter
instead. I'll also power the whole thing from a 12v battery. I'll still need
common ground for the MAF sensor return. I really don't need a perfectly
noise-free signal. A small amount of noise can be averaged out in my
analysis. But I'm currently seeing close to 1v P-P of noise on my 5V signal.
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