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Subject: Re: ph meter using PIC??
Date: Tue, 24 Sep 2002 07:44:35 -0400
Organization: Sprint Advanced Network Services
NNTP-Posting-Date: Tue, 24 Sep 2002 11:44:40 +0000 (UTC)
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.8) Gecko/20020204
> I would like to construct a phmeter using a PIC to control the water in my
> aquarium. I only understand that there are glass and epoxy electrodes. Can
> the electrode be made? How does it function? Any advice would be apreciated.
High sensitivity pH sensors are notoriously difficult to construct
and they drift a lot. In the aquarium you are trying to measure
minor changes in pH. There are some "stable" industrial pH sensors,
but their stability relies on measuring a wide pH variation;
essentially the drift is still there but it is small relative
to the range being measured.
The standard, high sensitivity pH meter works by having a
tube filled with electrolyte and two metal probes in the liquid.
A semipermiable barrier is made through the tube and that allows
the ions in the external liquid (your aquarium water) to influence
the conductance of the internal liquid. The meter attached to the
probe reads the conductance of the internal electrolyte.
In a dirty environment like an aquarium the barrier will become
clogged pretty quick, so it would require constant flushing.
I wonder if there is a good infrared spectrometer way to do
this pH measurement? I was looking into that about 15 years ago
and never found the perfect spectral wavelength for it. The idea
here is that the aquarium liquid is sampled for its absorbtion
in a narrow band of the infrared. This band would be at a
wavelength of absorbtion of some indicator compound that is added
to the water in a known concentration. The abosorbtion of the
indicator compound would change, dependant on the pH. The
absorbtion would indicate the pH. This would allow a flow-through
pH meter that didn't use the old method of a semipermiable
I saw some flow-through spectrometers being sold several years
ago. They didn't mention the ability to do pH, they were
mostly for juding organic matter content of the water.
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