Geoff,

Even professional instruments show substantial DC drift.  Broadband 
verticals have an output proportional to the rate of temperature 
change and over a 24-hour period can easily vary by a volt or more 
depending on their thermal insulation.  We routinely put in a 
one-pole digital high-pass filter at the lowest freqency available 
(0.002 Hz in WinSDR) which makes all that go away.

Sometimes an analog high-pass filter is used, but those can have a 
very long settling time and sometimes have their own problems, so 
they are generally used only when there's no good digital alternative.

Regards,
Brett


At 03:15 PM 12/23/2012, you wrote:
>I have tried every op amp circuit I can imagine as a preamp.
>
>Yet I can not rid a small DC drift which is either related to
>ambient AC noise level or DC drift of resistance or
>thermocouple voltage related to the soldering of junctions.
>
>This DC drift is related to the 24 hour cycle.
>
>The dc drift is on the order of microvolts
>which seem to be originating on the input.
>
>The overall DC gain is 80Dbv or X10000.
>
>I should be able to achive a DC free drift at this gain.
>
>I am using a op177G op amp ??
>
>The sensor is HS10-1 Geophone.
>
>The 40 foot of cable is designed for burial
>it has silicon grease (I think) impregnated and
>has a heavy copper jacket.
>
>It is soldered at the geophone and also at the sensor
>has soldered connections.
>
>Reply to this only if you have dealt with such an issue yourself.
>I do not want speculations since I swear I have tried
>every Uncompensated DC design I can imagine with not being able
>to stop this drift. No matter what the design the drift is
>the same increasing from morning to afternoon to the + plus
>and returning to adjusted baseline in the evening.
>The only remaining scheme is a capacitor input AC design ??
>Which i did not want to do.
>
>At the moment I rely upon Winquake to filter out the 24 hour DC drift.


__________________________________________________________

Public Seismic Network Mailing List (PSNLIST)

To leave this list email PSNLIST-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.