Increase  the gain till you get noise
like +/- 4 or 5 counts.

depends upon your A/D resolution.

With 9 bits you might need X10,000
With 16 bits you might need X300

It depends on how noisy your location is.

Cheers,
geoff
----- Original Message ----- 
From: "Ted Channel" 
To: 
Sent: Monday, August 01, 2011 1:24 PM
Subject: Amplifier op amp gain


> Hi Folks,   We have  been working on a simply cheap, seismic sensor 
> amplifier.  Just an op amp and a few components.
> 
> We seem to have it working, and so far so good, We are using the Arduino.
> 
> Now we need to decide, what gain it should be.   There maybe no one answers. 
> On professional amplifiers, like Larry's board, there are several gains 
> avail via the pot and jumper.
> 
> This will be fixed resistor, so for now I will limit my question to this.
> Q.  Is there a down side to too much gain, is there some sort of trade off, 
> if you use a large gain, say 2000, do you give up something, like drift, or 
> clipping etc.
> 
> I know very little about op amps and these values.   The coil in question is 
> approx. 970 ohms.
> 
> I have tested it with op amp gains of approx.  60, 80, 100, 150, 220, 470 
> and even 1000.   I could pick any of these gain, as they all seem to work, 
> and leave it at that.  I have a nice coil and magnet arrangement, so I don't 
> need a lot of gain.
> 
> Thanks, Ted 
> 
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