From: Geoff 

To: psnlist 
Sent: Sun, 23 Dec 2012 20:17
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.

Hi Goeff,=20

    If you use a CAZ type opamp like the LTC1150 you will get zero temperat=
ure drift.=20
Use a DIL socket soldered to your board, grease the pins of the opamp with =
Vaseline=20
and simply plug it in. Soldering it in can make an opamp noisy, if you heat=
 it too much.=20
    Why are you using so much gain ? Geophones normally require much less.=
=20
    Look up the OP177 spec ! Which one are you using ? The G version drifts=
 1.2 micro=20
V / C Deg ! !=20
    Regards,
    Chris Chapman =20


=20
From: Geoff <gmvoeth@gma=
il.com>



To: psnlist <psnlist@..............>


Sent: Sun, 23 Dec 2012 20:17


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.

Hi Goeff,=
 



    If you use a CAZ type opamp like the LTC1150 you will =
get zero temperature drift. 

Use a DIL socket soldered to your board, grease the pins o=
f the opamp with Vaseline 

and simply plug it in. Soldering it in can make an opa=
mp noisy, if you heat it too much.=
 

    Why are you using so mu=
ch gain ? Geophones normally require much less. 

    Look up the OP177 spec ! Which one ar=
e you using ? The G version drifts 1.2 micro=
 

V / C Deg ! ! 

    Regards,

    Chris Chapman<=
/font>