Hi Geoff,

Just an observation,=20
from the OPG177 datasheet, " The ultralow VOS of the OP177 combines with =
its
exceptional offset voltage drift (TCVOS) of 0.3 =ECV/=B0C maximum "
How stable is the Op-amps temperature environment ?
As you mention, capacitor coupling may be the best solution. I have used
200uF NP capacitors with OP27's to block tiny DC variations.

Regards,
Dale

-----Original Message-----
From: psnlist-request@.............. =
[mailto:psnlist-request@...............
On Behalf Of Geoff
Sent: Monday, 24 December 2012 7:16 AM
To: psnlist@..............
Subject: Instrumentation Question

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.










Hi =
Geoff,



Just =
an observation, 

from the =
OPG177 =
datasheet, =
" The ultralow VOS of the OP177 =
combines with its exceptional offset voltage drift (TCVOS) of 0.3 =
=ECV/=B0C maximum "

How stable is the Op-amps temperature environment =
?

As =
you mention, capacitor coupling may be the best =
solution. I have used 200uF NP capacitors with OP27's to block =
tiny DC variations.

Regards,

Dale



-----Original Message-----

From: psnlist-request@.............. [mailto:psnlist-request@web=
tronics.com] On Behalf Of Geoff

Sent: Monday, 24 December 2012 7:16 AM

To: psnlist@..............

Subject: Instrumentation Question

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.