There's one listed at http://www.globalw.com/wquality.html but at
$600 it's a little more expensive than free - may be a starting point in
your search.
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.
>http://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
======================================================================
Electronical devices for chemical laboratory, custom electonics design
----------------------------------------------------------------------
Snail Instruments Josef Hanzal
Vojanova 615 phone/fax: +420-311-24433
266 01 Beroun e-mail: spam_OUTsnailTakeThisOuTiol.cz
Czech Republic URL: http://www.vitrum.cz/snail/
======================================================================
Hi Josef and All
Thanks to everybody for your letters. Aquarium fish is one application.
Another is ponds. In Florida we occasionally experience large fish kills,
a whole pond will die for lack of oxygen. If you know the oxygen is low
it's easy to add more with a fountain or aerators but it's the not knowing
that drive you nuts. An inexpensive little probe with a sensor, PIC and
LCD would ease the minds of many folks...not to mention millions of fish.
----------
> From: Josef Hanzal <.....snailKILLspam@spam@IOL.CZ>
> To: PICLISTKILLspamMITVMA.MIT.EDU
> Subject: Re: [OT] Dissolved Oxygen Sensor
> Date: Friday, September 25, 1998 2:38 PM
>
> >http://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 {Quote hidden}
> your application ? Aquarium fish ?
>
> Josef
>
> ======================================================================
> Electronical devices for chemical laboratory, custom electonics design
> ----------------------------------------------------------------------
> Snail Instruments Josef Hanzal
> Vojanova 615 phone/fax: +420-311-24433
> 266 01 Beroun e-mail: .....snailKILLspam.....iol.cz
> Czech Republic URL: http://www.vitrum.cz/snail/
> ======================================================================
>> If you know the oxygen is low it's easy to add more with a fountain or
>> aerators but it's the not knowing that drive you nuts.
>
> Too expensive I suppose to just run the fountain periodically?
>From what I know things are not that simple. If you run the aerators (in
winter) too often, the pond may cool to the point, when the fish dies from
the cold, eventually the pond may freeze up all the way to the bottom. So
the measurement of oxygen level is necessary to run aerators only as often
as needed.
I will try to get some data from the sensor manufacturer on tuesday, will
let you know then. Hope you will have it ready before winter comes.
Josef Hanzal
======================================================================
Electronical devices for chemical laboratory, custom electonics design
----------------------------------------------------------------------
Snail Instruments Josef Hanzal
Vojanova 615 phone/fax: +420-311-24433
266 01 Beroun e-mail: EraseMEsnailspam_OUTTakeThisOuTiol.cz
Czech Republic URL: http://www.vitrum.cz/snail/
======================================================================
>> If you know the oxygen is low it's easy to add more with a fountain or
>> aerators but it's the not knowing that drive you nuts.
>
> Too expensive I suppose to just run the fountain periodically?
>From what I know things are not that simple. If you run the aerators (in
winter) too often, the pond may cool to the point, when the fish dies from
the cold, eventually the pond may freeze up all the way to the bottom. So
the measurement of oxygen level is necessary to run aerators only as often
as needed.
> Question: How did fish survive for millions of years before
> they invented electrically pumped fountains?
They didn't, that is not all did, but it took the interest of people with
some money in nice dinners to improve their fare (temporarily of course).
BTW, for occasional dip-in measurements, the ion exchange membrane sensor
is perfect, that's what it was made for. However it needs to be cleaned
regularly, inner electrolyte changed, washed as per manufacturer's specs
in destilled water etc. This is not something for people with no
laboratory cleanliness requirements training.
There SHOULD be a method to measure almost anything chemical by using an
electro-optical effect (i.e. polymer or crystal that dissolves oxygen from
air or solution and changes some electro-optical property, or epsilon),
but I know of no such thing off the shelf.
>> Question: How did fish survive for millions of years before
>> they invented electrically pumped fountains?
> They didn't, that is not all did, but it took the interest of people
> with some money in nice dinners to improve their fare (temporarily of
> course).
My muse really was that whilst an closed-loop control is the obvious
approach and could compensate for unforseen algal blooms etc., an open-
loop system using easily quantified predictors such as time-of-year, day
length, temperature etc., might be easy enough to implement.
--
Cheers,
Paul B.
iol.cz
