At 02:00 PM 4/8/98 +1000, you wrote:
>On Tue, Apr 07, 1998 at 10:00:26PM -0500, Bob Fehrenbach wrote:
>
>>     Far out idea #1.
>>     If the chemical content of the water is constant, you may
>>     consider the possibility of measuring the conductivity
>>     between two vertical metal rods.
>
>Hmm, it's rainwater, so it's probably both not constant, and very low.

Add another very short sensor rod attached to the end of an insulated rod to
get it near the bottom of the pool equidistant from the long conductive
rods.  Set this up in a bridge configuration and drive it with a current
source.  Amplifiy the bridge output with an instrument amp and A/D the
output of the amp.  Haven't tried this - just an idea.

The third probe is used to calibrate out the variation of the rainwater
conductivity.

Rich

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