Capacitive water level sensor

Yes, feasible.

You'd have to shield and compensate against outside influences (hand, bird landing on container, dirt, dust, rain etc.).

You can, but it should be possible without. The rod might corrode even if stainless, or at least gunk up.

For stuff like this I'd use sound, little piezos fastened at the desired levels.

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On Mon, 12 Jun 2006 23:33:58 +0100, Electric dabbler wrote: [about water level sensing in plastic container, 3mm walls ...

How about sonar? Stick little piezo elements to the plastic, and put each one in an oscillator circuit, and when the resonant frequency changes, the water level passed the element. Or maybe just the phase shift would change - you'd need to do some experiments, but it'd probably be less hassle than capacitive through 3mm of poly.

For capacitive, I'd put _some_ kind of conductor inside the tank, and probably put the copper strip vertically, and use the change in C as the indicator, but I'd think that'd have to be awfully sensitive. (read: hard to do and make stable simultaneously. ;-) )

Good Luck! Rich

I am interested in the same thing and found a dev baord and chip at

I never ordered the unit and the website has changed A LOT. In any case they had several designs for exactly what you want to do. Soem used a piece of PVC pipe immersed in the tank as the sensor.

Bill

I like the cork on a leadscrew turning a pot.... like they use for outboard gas gauges... or a cork with a magnet floating past some reed switches.

Looks a little complicated, so many variables. If you like challenges I would suggest hanging a closed stainless steel (or plastic) tube on a load cell and using Archimedean "Eureka!" principle deduce the water level by the reduction of weight. Linear from zero to whatever.

Good luck

Stanislaw Slack user from Ulladulla.

of

the

There is a commercial product, the Robertshaw Level Lance that does just about what you want. It is basically a 555 timer that uses the capacitance of the liquid rising and falling along a teflon-coated conductor as the timing capacitance. Only problem is that their calibration is only relative, you have to set it in the actual fluid.

Still, it is a commercial product using approximately the principle you have outlined.

Can you use the container's weight?

Set it on a platform equipped with strain gauges. Or, if this is a budget job, cannibalize one of those electronic bathroom scales.

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Not only is it possible, it is a commercial product. Google [capacitive proximity sensor].

Yes - Snake River Electronics

makes tank level sensors using this technique.

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Aquagauge low-cost capacitance water level sensor at

I made a probe by driving a copper pipe (tight fit) inside a PVC pipe, capped on the wet end.

A wire cage around the outside of the PVC (about an inch away) made connection to the water (ground).

Worked just fine.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

[snip]

I've often pondered using a piece of PVC pipe as if it were an organ pipe, driving it with a speaker, finding its resonance, and determining depth from that.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

"Electric dabbler" wrote in news:F8Gdnb snipped-for-privacy@bt.com:

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.

Analog devices have some ultra high resolution capacitance sensors newly introduced.

--
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Jim Thompson wrote: > I've often pondered using a piece of PVC pipe as if it were an organ > pipe, driving it with a speaker, finding its resonance, and > determining depth from that. >

Would that be an acoustic TDR?

GG

No; more like an acoustic LC bridge or grid dip oscillator.

Resonant cavity. :-)

Or, a 1/4 wave waveguide stub. ;-)

Cheers! Rich

Hello,

Thanks for all your really useful replies - I love the idea of sound!

Bill - the Quantum Research ic's look really interesting - I feel the urge to build something with a touch controlled front panel!

I have just glued two piezo elements to a large plastic water canister. I have no idea of their characteristics but they are identical and I can have fun working out what works best..

Thanks again guys,

Philip

Then you would need to compensate for humidity/temperature I guess ..?