On 5/10/2010 9:18 AM, Marcel Duchamp wrote:

> You are very close to the answer.  Try removing R9 - this will change
> the gain of the input amp from +2 to +1.  With an offset adjust value
> around +1V, you should get what you are looking for.
>
> Why the change?  You have an input voltage range of -2V to +2V ==>  4V
> span.  You want an output span of +4V to 0V ==>  4V span also.  Thus, you
> need a system gain of -1 which your second stage already has.

Sairam, by now, you have seen several conflicting suggestions.  I still 
stand by what I wrote.  I knew of the common mode range versus power 
supply levels limitation but it was my impression that you were 
successful with using it with the ORP application.  That may have been 
incorrect on my part.  But if you were successful before using it then 
it should work here as well.  It is something for you to look into to 
verify correct operation.

The data sheet is quite clear about unity gain operation.  There should 
be absolutely no problem with that.  Removing R9 will indeed make the 
first stage function with a voltage gain of unity.

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