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NNTP-Posting-Date: Sun, 12 Jan 2003 01:22:07 -0600
From: Barry Lennox
Subject: Re: Water sensor
Date: Sun, 12 Jan 2003 20:24:14 +1300
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On 10 Jan 2003 08:46:35 +0800, Bruce Murphy
>I've got a couple of applications that I would like to start building
>prototypes for but I realised that I'm outside the my realm of
>experience in one critical component -- water sensors.
What sort of time constant are you looking for? I have done a lot of
work recently with soil moisture sensors, and one of the simplest,
cheapest and more succesful is the so-called gypsum block, really just
two wires set in a gypsum block. Put the wires in a mould and pour
plaster of paris over it. You must measure the resistance with AC.
They make a small neat sensor, but have a time constant of probalby
several hours. OK for seepage building up into a puddle, but not for a
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