Monitoring Water Level in a Tank

One way to dispense water is to have a container high up of it which is sealed at the top by a two-hole cork.  One tube has a solenoid that connects to the atmosphere.  It is a normally closed type.  It is normally under the suation of a controller, but it also has a push-button manual override. 

The other goes to a flexible tube which acts as a siphon.  Hold down the button and suck, pulling your tube over the reservoir.

The reason to do it this way, maybe, is that your solenoid is operating on air rather than water,  which can be easier.

If even head is important, you might want to suspend your reservoir on a spring.  I can't find the exact literature, but I know some people have had success in weighing stuff by putting their payload on a spring and treating the spring as an inductor.

http://www.ti.com/lit/ug/snau150a/snau150a.pdf

Back in the days of working in the Oil Industry, I came across a level meter that used air.

The pressure required to release an air bubble(s) was used to determine the level in the tank.

Since it wasn't our device, I never did get all the details but it was safe for many types of liquid.

I've always thought it was clever because you can't loose product due to a fitting failure, and nothing sensitive is in contact with the product.

Mark

Back in the days of working in the Oil Industry, I came across a level meter that used air.

The pressure required to release an air bubble(s) was used to determine the level in the tank.

Since it wasn't our device, I never did get all the details but it was safe for many types of liquid.

I've always thought it was clever because you can't loose product due to a fitting failure, and nothing sensitive is in contact with the product.

Mark

I recall experimenting with a similar system in early childhood. . .

That would be a fun system to reproduce.

That would be a fun system to reproduce.

The more I think about it, the more it becomes clearer.

The guage was mechanical and had two set points (low and high).

There was a small pump which ran at some point/timed, and the line (from a hazy memory) was 1/4 plastic similar to a fish tank.

If you provide low volume air into the line, it requires x pressure before air flows.

The pressure is relative to the head of liquid above the outlet.

As the tank level drops, the pressure reduces ... air leaks out until the two are balanced.

As the tank refills then the pressure increases and liquid will flow up the line.

If the pump starts then the liquid will be displaced and the same pressure remains.

So if you had a small air pump (fish tank) and a pressure sensor, you should have the basics of a monitoring system.

You just need to calibrate it.

Mark

Hi Mark,

It occurs to me that in hydroponics the water must be aerated before application.  The leaves of a plant have chlorophyll and ATP and stuff to get energy from the sun and split CO2, but the roots respire like an animal or a fungus and are similarly susceptible to asphyxiation.  So roots need water with oxygen dissolved into it, like fishies do.  So, this means that a fishy pump is often already present in this case!

I don't know whether I would have ever transferred this idea from the bathtub!  Thanks, it is probably as practical as it is amusing!  I think this would even work for for relatively viscous liquids.  That was probably an incentive for its use in the petrol industry, that and it seems far less messy to clean up than the linear sensors alluded to up in this thread if we are dealing with a thick, composite, organic liquid.  6AM, and you have already made my day!  It is neat to imagine that you could use the pressure sensor both to monitor the increasing pressure and the relieving, discrete event of the bubble leaving for points beyond.

I don't think gauge pressure sensors cost too much anymore, they were a little dear when they first came out, so this should be a practical, realizable thing in some applications.

Gentleman,

in this project there is no pressures or pumps allowed in the procedure.  The system must operate by gravity.

The water used or leaving the lower tank (see diagram above) is saturating material located under the tank.  the saturation is slow process (The process time is at least six hours. so there is at least 12 readings, when filling the refilling the tank every 30 minutes ).  Evaporation from both open tanks is allowed.  Accuracy is only to 1/8" in readings.

The controller clicks the valve open  until the depth recorded by the sensor is 15 inches then the valve is clicked to close.  The depth data (water level dropping) is then collected by the sensor every 30seconds for 30 minutes.  Then the valve is clicked again to fill the tank back to the 15 inch mark and closes.  The second set of depth data is collected for 30 minutes.  This loop is done 12 times.  The above minutes and depths varies (selected by the tester at the start of the process).  Reading may be taken every second or every minutes, etc.

Don

I have a book on Hydroponics and we were set to do an article (well until the major supplier was busted for selling it for the wrong reasons ).

I'm no expert but the non saturated roots system tends to be favoured more than the total immersion in water.

Various things are measured and if the returning water falls into the collection container, oxygen is imparted just like a stream or river.

The Oil industry require "intrinsically safe" devices, which means various processes to limit the energy available where there is product.

Since air is not an energy source and the pump is a distance away, it requires no testing or proving in order to be used in either diesel or petrol.

Yes electronic pressure sensors are very cheap and readily available now, so this is a project I need to add to my list.

Mark