Craig Webb wrote:

> Thanks for the help. I'm running at about 2000 samps/sec (though I'd like to
> run 8 channels!). We'll see how it goes. Some good suggestions though. How
> many bytes would you use to keep good resolution at 13 bits? The person I'm
> working with who has already written some LPF code said we need four byte to
> keep precision. This seems a bit high to me.
>
Craig,

I posted the following a number of months ago in response to a similar
question.

First, you have to know the "noise-free" counts of your system.  This is
typically your full scale signal divided by 6 times the rms noise - you
find the rms noise by calculating the standard deviation of a sample set
(I use a minimum of 1000 sample points).  Of course, this is only valid
if your noise is Gaussian - plot your sample set to see.  Where did that
"abritrary" value of 6 times come in?  If your data plot indicates that
your noise is Gaussian, one standard deviation is equivalent to the rms
noise.  Almost all of the data points will fall within +/-3.3 standard
deviations - use a factor of 6 (close enough to 6.6) to estimate the
peak-to-peak noise relationship to the rms noise.

NOW, you can use averaging to improve system resolution.  BTW, thermal
noise is typically the only true Gaussian noise that you're going to
find.

--Matt