yamanoor sairam wrote:
> I am currently trying to use the same op amp circuit to modify such
> that I am able to read signals from probe between -2V to +2V. I
> wanted to level shift the signal such that I am able to read the
> signal against a scale of 0-4V. I removed the 40K resistor
> http://mechatronicscraze.files.wordpress.com/2010/03/orp-circuit1.jpg

There is much wrong here.  The most serious problem is that these opamps are
intended to run from a wider supply range, and have rather large headroom
requirements for both input and output.  The datasheet is vague on what
happens when you power them at only +-5V, but at +-15V they require 4V
headroom for input signals and 3V for output.  This is not likely to get
better with lower supply voltage.  You therefore should figure these amps
are good for +-1V input and +-2V output in your application.

As for the 40K resistor (I assume you mean R16), that together with R9 sets
the gain of the input stage.  Removing it makes the amp function as a
comparator around 0.

It's obvious you're just guessing how this circuit works.  You can't make
meaningful changes until you do.  First I suggest ditching the TL072 in
favor of something with less headroom required, such that it can do useful
things with +-5V supply.  Fortunately there are many opamps that fit that
requirement.  Next, find a basic text on electronics that covers opamps and
read it.  Don't do anything until you understand how your original circuit
was supposed to work (ignoring the headroom limitations of the TL072).  Then
read the datasheet of whatever opamp you chose carefully.  Only then are you
ready to make modifications to this circuit.


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