Is there a way of having a 'stick' hit the container and some sensors liste=
n for the 'ring' of the cavity inside?

I'm thinking here of the way to check the level of gas in a gas bottle and =
see if it rings or is damped.

You could have a couple of 'sticks' and a couple of sensors at around the c=
ritical point you want to measure.

I'm thinking a sensor like a crystal microphone where you could arrange a p=
in from the diaphragm to be in contact with the outside of the container, y=
et still be a rugged sensor, and a spring loaded stick that could be pulled=
 back by an arrangement similar to a hammer in a clock that strikes a bell.

I'm guessing it probably only needs to operate about 4 times a day to get a=
 sense of the content level.



> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of James Cameron
> Sent: 26 August 2016 11:34
> To: piclist@mit.edu
> Subject: [EE] external liquid sensing, through 4mm plastic?
>=20
> Living in the outback ...
>=20
> Looking for a way to estimate liquid levels on the other side of 4mm plas=
tic; a
> potentially flammable methane-air atmosphere, without necessarily cutting
> holes in the plastic.
>=20
> Composting toilet collection bin has a coarse filter 50mm from the void a=
t the
> base, and a liquid drain.  A DC fan pulls air through the bin contents, t=
hrough
> the void, into a chimney.
>=20
> Composting works best when the void has less than 20mm of liquid.
>=20
> Sometimes the drain becomes blocked.
>=20
> Liquid levels increase slowly, blocking the airflow, until the gas genera=
tion of
> the bin contents exceeds the airflow, then the residents really notice.  =
Pong.
>=20
> How to measure the liquid level?
>=20
> Float switches would become fouled.
>=20
> IR reflectance sensors would be great, but expensive, and if covered by
> muck wouldn't reset until the bin was serviced.
>=20
> Stainless steel bolts through the plastic might work, but there's a condu=
ctive
> path through condensate on the inside surface.
>=20
> "Can't you just point an instrument at the tank from the outside and have=
 it
> tell you the liquid level?"  ;-)  Magic is wanted.
>=20
> --
> James Cameron
> http://quozl.netrek.org/
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

--=20
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