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Subject: Re: Water sensor
References: <firstname.lastname@example.org> <email@example.com>
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NNTP-Posting-Date: Tue, 14 Jan 2003 16:15:06 GMT
Organization: Insight Broadband
Date: Tue, 14 Jan 2003 16:15:06 GMT
On Tue, 14 Jan 2003 09:20:57 +0000 (GMT), Tony Williams
wrote in message
>In article ,
> Bruce Murphy wrote:
>> Tony Williams writes:
>> > 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.
>> While this is a cute idea, since the sensors have to be small, this
>> strikes me as replacing one hazard with another.
> It's a cheap (and cruder) version of what is
> used for oil-level sensing in gearboxes, etc.
> In that app the thermistor resistance is measured
> at low power, then it is given a high power for
> a fixed time, and the resistance measured again.
> (T1 - T2) determines whether the thermistor is
> immersed in oil or in air. Widely used in the
> automotive and avionics industries... there are
> even ic's to do the job.
You also need to measure temperature because thermistors are 'notorious' for
changing value with temperature ;-) One way is to use two thermistors, one of
which is always submerged (or not) and in same temperature/heat conductance
In 1985 or so I presented a paper on a thermistor-based method to assess oil,
water and air saturation in porous media such as sand based on both static and
heat pulse measurements. The latter provides a waveform which contains more
information for interpretation than two static measurements.
Do you know of a replacement for the now-discontinued LM1820 Fluid Detector IC?
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