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From: Tony Williams
Subject: Re: Water sensor
Date: Fri, 10 Jan 2003 14:00:30 +0000 (GMT)
NNTP-Posting-Date: Fri, 10 Jan 2003 14:01:09 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
Bruce Murphy wrote:
> Ideally these would be as simple/cheap as possible -- one of the
> applications involves a sensor array to detect various critical water
> events for airconditioning that has been installed far too close to
> equipment I care about.
How about a small PTC Thermistor, powered by a
voltage large enough so that the temperature of
the thermistor exceeds 100C in air. Monitor the
current drawn for a measurement of its resistance.
When in water the thermistor will struggle to get
above 100C as it tries to evaporate the water off
(540 cals/gm?). At that point its resistance will
be stuck down at the 100C value.
Use one current shunt, switched around the sensors.
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