Ok, This is my lesson for the day to read responses better. Obviously I was
answering completely the wrong question from Mr. Ewald. Here is a better
response:
The use of accelerometers in automotive applications I've seen have to do with
vibration measurement. The problem is its really hard to properly filter out
noise/harshness issues in a car due to their inherently wierd nature (random
external inputs, variable frequency excitation due to engine RPMs, etc.) so you
end up having a real bear of a time trying to do signal conditioning. You end
up
having to not filter as much in order to get the data you want, and hence end up
with more erroneous signals due to these wierd external inputs, etc. Generally
the noise in automotive applications is sufficiently bad you don't want to use
sensitive devices in a consumer version. Also you have to worry about
calibration
and drift, which can't be compensated for very well on the fly.
Anyway, thats my little bit for the day. Sorry for the off topic discussion...
A. Arabian
REwald9535@aol.com wrote:
> In a message dated 01/21/2000 10:57:47 AM Pacific Standard Time,
> arabian@allegronet.com writes:
>
> > A number of cars use accelerometers, but NOT for axial deceleration
> > measurement
> > generally. They are for lateral acceleration - i.e. cornering. The ABS
> > operates slightly differently when cornering than when going straight (more
> > braking on the inside wheels I think, but I could be way off base on that.
> > Don't remember the specifics). Anyway, my guess based on my limited
> > measurements experience is that accelerometers (or at least reasonably
> > priced
> > ones) are just too noisy to be used very well for axial deceleration.
> >
> As far as I know no ABS system uses accelerometers. the wheel speed sensor
> uses a toothed wheel and some type of pickup (magnetic is the most common) A
> magentic sensor generates a sine wave and the signal goes to an analog to
> digital converter (typicaly a Schmit trigger) this A to D converter may be in
> the control unit on in the sensor. The control unit is just looking at the
> frequency of each wheel and calculates G force from changes in frequency of
> each wheel.
> Accelerometers are used in yaw control systems, my company car has one. I do
> have one question, your comment about noisy? The sensor in my car is solid
> state and as such is stone silent. How do the ones in your experience work?
> Rick Ewald
|