On 10/13/2011 7:33 PM, Randall Pratt wrote:
> I am getting strong spikes at about 48 second spacing for the last week or
> so.  I suspect my power supply but have not confirmed yet.  It began shortly
> after moving the instrument and adjusting the zero output level.  I have
> posted pictures at http://mit.midco.net/rpratt/   The top graphic is a
> WinQuake view at 12 sps.  On the bottom is a Windaq trace at 240 sps showing
> the spike as a short oscillation followed by a smaller wave.  If I look at a
> series of spikes I see they fall into 2 types with one going up first and
> the second down first but they do not always alternate in that pattern.  FFT
> of the 240 sps trace also shows some 60 hz coming through.   Does anyone
> have any thoughts?
>
>
>
> Randy
>
>
>
>

Grounding and shielding is of utmost importance in eliminating 
electrical artifacts.
It is not easy to do unless you have built your own system.
You are pretty much at the mercy of the manufacturer.

Tie everything possible to a common ground.
Set your sample rate above the antialize filter
and keep it there.
Shield everything between the computer and ground.

The concept is to create an iso voltage environment allowing the
only differential AC signal to be the seismic signal.

You must also eliminate the possiblity of ground loops of current flowing.

I think it is called GROUNDING and BONDING.

If you do this than you can be sure other factors are
causing the spikes.

Power line hum is difficult to completely eliminate
or at least for me thats true.

It requires understandings beyond myself.

I am not an Engineer. Just a layman who plays one from time to time.

If you can walk by the electronics, blow on it with your breath,
Touch the boxes & cables  holding the circuitry, with no noticable
effects on the trace. It should be shielded fairly well.
A real test would be a blast with a heat gun then cold spray.
Scrape your feet on the carpet and touch the circuit ground ???
But thats silly for the common user to have to do.

Regards,
geoff





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