Bernard Tyers wrote:
>Hi all,
>
>first post.
>
>I am trying to use a CA3140E op-amp as a comparator.
>The two inputs are chemical sensors. The difference voltage between them
>can range between 400mV, to 50mV (100% concentration to 0% concentration).
>
>I remember reading somewhere in a text book, that if V1-V2 is greater than
>(I think) 100uV the op-amp will go into saturation.
>
>Can anyone a) clarify this for me, or b)suggest a better way to measure
>the difference voltage.
>


Hi Bernard - I added a topic to your header. With opamps, you "always"
use them in feedback configurations if you wish to do anything useful
with them. Sounds like what you want is a difference amplifer ckt.

For theory, try searching google.com on "difference amplifier", or
try here [mind the URL wrap]:

http://www.inform.umd.edu/EdRes/Topic/Chemistry/ChemConference/Software/
ElectroSim/Subtractor.html

For accuracy, use 1% tolerance [or better] resistors in the ckt.

hope this helps,
- dan michaels
www.oricomtech.com
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