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Measuring Conductivity with ADC

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Newbie level 4
Oct 21, 2009
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I need to find a way to measure the conductivity or resistance of a liquid using a microcontroller with an output of 5vDC. I also need to use no more than 1vDC to do so.

So far I have tried reducing the output to 0.8v and using an opamp on the ADC input to amplify the return. I cannot seem to get it right no matter what I do. Can someone point me in the right direction on how to accomplish this or show me an example? Maybe I am going about this all wrong? Thanks!

It will be more meaningful if you could add some more information to clarify your actual proble. Any suggestion on altogether new lines could be repeating what you have done in a different area.

I guess, you know that conductivity is an AC measurement, if it should have any quantitative relevance?
Thus it involves a somewhat complex circuit: Generator, source/sense amplifier, demodulator or rectifier.

Or are you just designing a kind of level switch without measurement accuracy requirements?

I need to measure the resistance of a liquid in order to determine the next steps in my program. I have gotten it to work by using 5vDC and using the voltage drop across the liquid to determine the resistance, however in my application I cannot use more than 1vDC to perform the check.

I tried using an op amp to amplify the return but it was very flaky and provided inaccurate readings.

DC voltage across the elctrodes causes electrode polarization and electrolysis of the liquid. It can't give reliable results.

So an AC signal would be the way to go? How would I approach it?

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