Randall Clague wrote: > > On Sun, 17 Nov 2002 16:11:32 -0800, David Weinshenker > <[EMAIL PROTECTED]> wrote: > > >> Total amplitude should be the same, though, right? > > > >Good question... sampling a signal with components of higher frequency > >than half the sample rate introduces weird "alias" artifacts; the answer > >to your question then becomes "maybe, but you really can't trust it even > >that far." A vibration with a frequency that's an exact multiple of the > >sample rate might cancel out completely, or appear as a steady high or low > >level, for example, depending on the relative phase of the signal frequency > >and sample rate. > > The chug frequency wasn't constant; we heard it changing pitch. I > think for reduction purposes we can assume the relationship between > the sampling frequency and the oscillation frequency is variable. > Given that assumption, aren't the amplitudes pretty much the same over > a ~100 msec time scale?
Not until I see a physically plausible explanation for that negative G (other than the engine chugging so hard that it developed an extreme vacuum in the nozzle?)... my guess is there was high frequency energy in there that tickled a mechanical resonance on the accelerometer chip (a bit over 1 kHz IIRC), and that gave a false high-amplitude signal that then got aliased by the A/D. (I don't know if the RDAS board has any signal filtering between the accelerometer chip and the microcontroller A/D input.) One way or another, it's clear that something ragged was going on there; we need to try to see what it takes to get the engines to run more smoothly. -dave w _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
