On 2012-12-24 1:29, chrisatupw@....... wrote:
> 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,
>
>
>
>      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 of the opamp with Vaseline
>
> and simply plug it in.Soldering it in can makean opamp  noisy, if youheat it too much.
>
>      Why are you using so much gain ? Geophones normally require much less.
>
>      Look up the OP177 spec ! Which one are you using  ?The G version drifts 1.2 micro
>
> V / C Deg !  !
>
>      Regards,
>
>       Chris Chapman
>
>
>

The problem does not seem to be the amplifier itself.
But rather, the variables dealing with the input.
Cable/Geophone/Common mode stuff/
Yet I have found a wide variation within the
op amp offset voltages.
I am currently using a Chopper amp (or so I think)
In the front end. LTC1050 ???
Yes, I have troubles finding decent opamps
at civilian prices, the best are all seem to be MilSpec
rip offs. Outrageous prices. The milspec parts are by far
the best and all others should simply be scrapped.
Or so i believe. if all you create are the best,
then the best will be the cheapest it can be.
The trouble here is, administrators treat human beings
like technicians treat inanimate things.
ripping off their bad opamp legs so they cant be used elsewhere
in other circuits in the future.
Regards,
geoff
LTC1050 - Precision Zero-Drift Operational Amplifier with Internal 
Capacitors
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