>www.vernier.com has lots of probes for sale, including a dissolved oxygen
>probe for $189. Not cheap, and it's a "finished" product, not just the
>sensor, but might be worth a look.

Most dissolved oxygen sensors are of Clark type. It is platinum disk covered
with thin polymer membrane, with some indiferent electrolyte (I believe KCl)
between the platinum and the polymer. There is also reference electrode -
silver wire covered with silver chloride conected to the inner solution. The
Pt electrode is kept at negative potencial of ~650 mV vs. the reference and
the current flowing between these two electrodes is measured.

As oxygen diffuses thru the membrane it dissolves and undergoes reduction at
the Pt electrode and the current is proportional to O2 concentration. The
sensor is also temperature dependant.

It is hard to believe that someone is selling these things for nothing...
But I believe about $50 could buy you something to start with. BTW, what is
your application ? Aquarium fish ?

Josef

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Electronical devices for chemical laboratory, custom electonics design
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