If you show the op amp circuit configuration I will be happy to explain how 
to do this.


----- Original Message ----- 
From: "yamanoor sairam" <yamanoorsai@yahoo.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Tuesday, May 11, 2010 3:47 AM
Subject: Re: [EE] Opamp design doubt


> Dear All,
>
> I have a question regarding the calibration of probes. As the ORP probes 
> age, they tend to lose their accuracy of reading due to the aging of 
> probes. The ORP probe's accuracy is checked using solutions that have 
> potentials in the range of +200mV, +400mV etc.
>
>
> Can I adjust the offset voltage using a precision trim pot to make small 
> adjustments in the offset voltage? Should I make minor adjustments in my 
> code for offsets in voltage?
>
> Yours Sincerely,
> Sairam
>
>
>
> ________________________________
> From: Marcel Duchamp <marcel.duchamp@sbcglobal.net>
> To: Microcontroller discussion list - Public. <piclist@mit.edu>
> Sent: Tue, May 11, 2010 4:52:37 AM
> Subject: Re: [EE] Opamp design doubt
>
> 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.
>
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
>
>
>
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
> 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist