On 12/24/2012 1:55 PM, Brett Nordgren wrote:
> 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.
>
>
If you located a seismometer AND its instrumentation within a
deep cave the temp might be a constant 65deg every day
of the year. Such a thing IS within the capability of the government. 
But not
the Amateur.
__________________________________________________________

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.