--- In "j.chitte" <> wrote:
>
> --- In "PeterElliot" <egroups@> wrote:
> >
> > --- In "j.chitte" <j.chitte@> wrote:
> > >
> > > Not getting anyway fast with this.
> > >
> > > I see continuous +/- 2mV which is expected 2LSB variations
> however
> > > frequent +/- 6mV spikes are spoiling my day.
> > >
> > > Nobody here tried to get accurate ADC on the 7250?
> > >
> > > Thx.
> > >
> >
> > What sample rate are you using? I tend to oversample and average
> my A/
> > D readings to reduce this type of spurious periodic noise. This
> all
> > depends on the signal being measured and the current sample rate.
> >
>
> Thanks,
>
> yes I can use a mean to reduce the peaks but I want to get noise down
> to a minimum before I start to paper over the cracks.
>
>
> > Without knowing the exact design, the causes for these noise
> spikes
> > are difficult to pin down, but if you're refering to the A/D on
> the
> > TS-72xx board itself I doubt that the layout was aimed at getting
> the
> > full performance of the A/D - I don't know if they implemented a
> > separate analogue ground plane around the chip, It may be that
> it's
> > picking up noise from the digital circuitry.
> >
> > PJE
> >
>
> I am starting to suspect that it's the ethernet driver loading the on
> board power rails.
>
> It's true the board layout could go further , this is why I was
> asking if anyone had direct experience of noise levels , this would
> help me see if it is a defect in my work or I am up against a
> limitation of the TS board.
>
> Some input from Technologic may be helpful here.
>
> Many thanks for comments.
>
> /jacques
>
Hi Jacques --
Are you sure your signal coming in is clean?
I guess you are running tests only a single channel, right, so no
settling time issues? What's your sampling frequency? You mentioned
'spikes'. Are the spikes periodic, and if so, what frequency?
I've seen noisy A/D in top-of-the-line National Instruments PCMCIA
cards when the laptop was charging: 60 Hz noise was coming in from
the cheap PS. Running the laptop off the battery or a lab-grade PS
cleared the noise right up. A noisy PS could affect your TS board and
/ or your signal conditioning board.
Your idea about the ethernet loading seems quite possible too. You
could confirm it with a 2-channel scope, or failing that, just turn
off the ethernet chip as a trial.
Regards, ....... Charlie
------------------------------------
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|