Contact less water level sensors

[mutthunaveen]

Dear Board

Im making a water level controller project for which i need your help.

so far what i ve done.
- the water im dealing with is salty water, too much scaling
- i ve built a water level sensing circuit with normal probes. due to scaling they stopped working
- i used stainless steel probes they also stopped working after few days -- all because of scaling (salt water)
- i used floats with read switches. Due to extreme temperature conditions the reed sensors glass are tend to fuse/break. and due to scaling they stuck

now i wish to upgrade to contact less water level senors, i ve seen in few websites. they are quite expensive. what i ve seen is a round sensor that will be placed on the side wall of plastic tank. the onboard LED glows when water is in tank else it goes off. this is what exactly im looking for.

(i know going with Ultrasonic is not a good idea for a overhad tank)

could you please suggest me if you have any ideas on DIY contact less water level sensors

Thank you
naveen

 

[BradtheRad]

Shine a narrow-beam led onto the surface of the liquid. It reflects back up to the lid of the tank. Mount a row of CdS photocells to the lid. Connect each photocell to a circuit that turns on a different indicator led.

Or rather than mount several photocells...
It may be possible to have the reflected beam shine on translucent plastic which creates a hazy spot, detected by a single photocell. Illumination on the photocell changes depending on its distance from the hazy spot. Detect current through the photocell, and display reading on a meter or bargraph leds. A 3914 IC (ten-step bargraph) is able to do this job.

 

[betwixt]

Another method is to use an external pipe fixed near the bottom of the tank so you can monitor from outside where it is environmentally easier. If the pipe is vented at its top, the level in it will be the same as inside the tank. From there you can use small capacitive sensors or even a floating magnet in the pipe operating switches outside it.

If you have to work inside the tank, the best method when corrosive materials are involved is to use insulated probes and measure the capacitance between them. For example wires inside narrow plastic pipes so they are not in direct contact with the liquid but AC conduction between them will be proportional to the depth of dielectric (the water) surrounding them.

Brian.

 

[FvM]

The term "scaling" doesn't seem to be a commonly understood technical term related to level sensors and salt water. Which problems are you observing exactly?

Can you clarify about the temperature and salt concentration range? Are you dealing with additional contaminations?

Popular continuous level measurement methods for wastewater are hydrostatic pressure and air bubbler, see https://en.wikipedia.org/wiki/Level_sensor

There are also very rugged float switch designs if you don't need continuous monitoring.

 

[vivekroy]

I am curious why ultrasound level sensors cannot be used for overhead water tanks? A cursory Google search throws up quiet a bit of products from Alibaba at less than USD 100. What is the issue with it?

 

[betwixt]

FvM, the term 'scaling' isn't technically correct and has nothing to do with multiplying or dividing. In context here it refers to the build up of chemical deposits on the electrode surface, rather like the 'scales' on a reptile skin.

Isn't language wonderful - one word and a thousand interpretations!

Brian.

 

[FvM]

In context here it refers to the build up of chemical deposits on the electrode surface, rather like the 'scales' on a reptile skin.

That's what I guessed, but I didn't hear the term yet in the context of level sensor specification. We have more specific descriptions of possible interfering stuff, e.g. sludge deposition, crystallization etc. Different sensor types have different resilience against specific disturbing effects, thus I'm asking for a substantial description.

 

[chemelec]

DC Causes Electrolysis between the Probes.
AC Might be Better, especially if a low current.

Besides that, there are Many Grades of Stainless steel.
Many of which or Very Poor Quality.

 

[Aussie Susan]

"Water scale' is a a common technical term in relation to water - https://www.wqa.org/learn-about-water/perceptible-issues/scale-deposits is just one of many Google search results.
Also consider words such as 'calcification' or 'hardness'.
Susan

 

[KlausST]

Hi,

AC Might be Better, especially if a low current.

Yes.
And a water level sensor usually doesn't need to work continously .... and doesn't need to be very fast.
Thus you may switch the electrodes high impedance most of the time, and activate them only when needed.

Maybe activate them just for 50ms every 1000ms... this may reduce the electric stress to 5%....and increase lifetime.

Klaus