Capacitive water level sensor

[Electric dabbler]

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

 

[Joerg]

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.

Yes, feasible.

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?

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

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'

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

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.

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

 

[Rich Grise]

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

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

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

 

[beananimal]

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.

I am interested in the same thing and found a dev baord and chip at
http://www.qprox.com/products/continuous_sensing.php

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

 

[BobG]

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.

 

[Stanislaw Flatto]

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

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.

 

[BFoelsch]

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

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.

 

[Paul Hovnanian P.E.]

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.

 

[John Popelish]

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.

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

 

[Peter Bennett]

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.

Yes - Snake River Electronics (http://www.snake-river.org/) makes tank
level sensors using this technique.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[John]

Aquagauge low-cost capacitance water level sensor at

http://www.electrosense.com.au

 

[Jim Thompson]

Aquagauge low-cost capacitance water level sensor at

http://www.electrosense.com.au

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

 

[Jim Thompson]

On Mon, 12 Jun 2006 19:11:02 -0700, Jim Thompson

[snip]

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

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

 

[Geoff C]

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.

 

[Don Lancaster]

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

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


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Glenn Gundlach]

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.

...Jim Thompson

Would that be an acoustic TDR?

GG

 

[mc]

Jim Thompson wrote:


Would that be an acoustic TDR?

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

 

[Rich Grise]

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

Resonant cavity.

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

Cheers!
Rich

 

[Electric dabbler]

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

 

[[email protected]]

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.

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