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      08-23-2008, 06:56 PM   #17
ArtPE
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Drives: e46 M3
Join Date: Dec 2007
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Quote:
Originally Posted by lucid View Post
Thanks Swamp. This is rather interesting preliminary data. I am looking forward to seeing more measurements taken at a higher sampling rate (300 Hz on the first graph seems to be just the bare minimum for capturing anything meaningful), and a comparison of the same shift, say 2->3, in D and S modes under WOT so that we can isolate any effects of your throttle input during the shift, which might not be constant (I assume that's why we are not seeing a significant drop in acceleration after the 2->3 shift, which should happen due to the change in gearing, or is it just the scale of the y-axis combined with the noise that makes it difficult to observe this?). I realize that is not easy to do on public roads though. Is there any reason why you are not using the 1kHz sampling rate? I believe the accelerometer will do that, right? And, yes mounting the accelerometer rigidly should decrease noise significantly.
300 hz is plenty...that's a sample every 3.3 ms...generally speaking you need to sample at 2x the frequency of the signal you are trying to capture data for...

so if the shift is 30 ms, 3.3 is 9x's...
3.3 is theoretically enough to capture 8 ms...

Nyquist-Shannon
If a function f(t) contains no frequencies higher than W cps, it is completely determined by giving its ordinates at a series of points spaced 1/(2W) seconds apart.
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