piclist 2000\05\31\163637a >
Thread: [PIC] How to measure level of liquids and sense relativehumidity?
www.piclist.com/techref/microchip/devices.htm?key=pic
BY : Mark Willis email (remove spam text)

Dan Michaels wrote:
> Mark Willis wrote:
> .........
> >What's wrong with a cheap and easy, hot bead thermistor solution,
> >though?  Constant current through a thermistor to intentionally
> >self-heat it to say body temperature or so, when in free air -  then
> >measure the resulting voltage - when water level rises to where the
> >thermistor is covered in water, it'll cool the thermistor in a heck of a
> >hurry, thus voltage change and you know the water's there.  Want the
> >water to not spray onto the thermistor, of course, placing the
> >thermistor inside a tube or if needed adding a tank water inlet baffle
> >will solve that though <G>  Yeah, it's contact sensing, I know.
> >
>
> Plus, I suspect you could use 2 or more thermistors arranged
> vertically within the tube, plus a little math, to actually
> determine the level, not just whether above/below one point.

True on multiple height determination - though (despite my being pretty
good in math) I don't see where the math's needed/applicable.  I thought
with 3 hot beads, you'd know one of 4 states, {"Height < A" || "Height
>= A" || "Height >= B" || "Height >= C"}, don't see how you can determine shades of height between say A and B (putting A lowest, C highest here, to clarify.)  Am I missing something?  Has been a "Bad Brain Day" to some degree <G>  (There's not a big difference for thermistor B in temperature, between temperature for water say 1 foot below it and 1 inch below it, barring splashing, is there?  Has been a while since I last hot-beaded <G>)

Mark

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