I designed a water level remote gauge for home/commercial tanks about
thirty years ago that had a vinyl tube with a weight at one end and a
pressure sensor on the other end. Throw the weighted end into the water
and the column of air becomes pressurized proportional to the water
depth. It does require a method of keeping the tubing free of water.=20

Left to itself, water migrates up the tubing. This takes a long time but
is inevitable! Even if you try to outsmart it with a large
bellows/balloon/etc.

So you put a tee at the sensor end and attach a fishtank pump with a
timer set to run for a minute every night.

About ten years ago I stopped doing it that way, switched to ultrasonic.
Waaaaay cheaper! It's a moist environment but drinking water isn't
corrosive and there's no splashes, just add lots of conformal coating to
everything except the transducers.

Cheerful regards, Bob

On Mon, Jan 26, 2015, at 05:15 PM, IVP wrote:
> (tag changed)
>=20
> I've used a 4-20mA depth gauge that measured to 6m to a
> couple of mm (their words)
>=20
> It was a long thin (6-7mm) yellow hose containing the wires and I
> believe a Honeywell pressure sensor at the sealed end. Comparing
> the output to a ruler showed it was pretty accurate, bearing in mind
> inaccuracies of the PIC's ADC
>=20
> Joe

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