Hi Geoff,

By "DC drift", do you mean that your traces are not centered on the zero 
Y line?  If not, how do  you observe that you have a "small DC drift?

Roger

On 12-24-2012 12:01 AM, psnlist-digest-request@.............. wrote:
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Instrumentation Question
> From:    Geoff 
> Date:    Sun, 23 Dec 2012 20:15:55 +0000
>
> 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.
>
>
>

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