Re: Capacitive water level sensor

"Electric dabbler" <no.spam@xxxxxxxxxxxxx> wrote in
news:F8Gdnb_WQcxWdhDZRVnyjA@xxxxxx:

Hi,



Is it feasible to sense water level in a plastic container with
capacitive sensors on the OUTSIDE of the container? The container
concerned will be a heavy gague plastic water storage vessel - perhaps
2 - 3mm thick walls.



I'm thinking of using some strips of 1" copper tape glued to the
outside
and attempting to sense the change in capacitance caused by the
presence of water at that level in the container. I suspect the
problem here is tha the change would be too small to reliably detect?



Alternatively I could immerse just one long stainless steel rod in the
container as one capacitor 'plate' and using single copper strips on
the outside at various levels. Here could energise the external
electrodes squentially and measure what comes back on the stainless
steel rod relying on the conductivity of the water to form the other
'plate'



I need to sense multiple levels and drilling holes in the container is
not really an option.



I'm not after a commercial solution, just a quick and dirty DIY
approach.



Your thoughts gratefully appreciated.



Philip



I have made the following with success if you want to DIY, similar to
Rich's idea.

Get 2 piezos which are identical. You need a certain defined thickness,
such as made by Phillips. They have a defined resonant frequency, eg.
2MHz for about a 1mm thick one. The principle is a transmitter, driven by
a Xtal oscillator at the same resonant freq, and a receiver on the other
side of the container. The piezos are placed on the outside of the vessel
and glued on the surface.

Electronics are easy. Transmitter is xtal oscilator and buffer. Receiver
is linear amplifier following recieve piezo, rectifier detector and
comparator or just a gate for quick and dirty. I made tx and rx with one
74HC04, using 1st recieve gate in linear mode. Was relaible and fluid can
be sludgy. Using this technique there is more difference than a
capacitive sensor for different fluid levels.
.

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