Water Tank Depth Sensor

[rthorntn]

G'day!

Apologies this might be more of a physics question than an electronics one.

I want to measure the water level in my 6ft high vented rain tank, I have the MPX5010DP differential pressure sensor and 25ft of hose.

Can I mount the sensor at the top of the tank and weigh one of the hoses down so it sinks to the bottom of the tank and have the other hose in the air above the water?

So the hose would be 6ft long and submerged straight down, I can't comprehend if the pressure sensor will actually measure the pressure at the bottom of a long hose...

Should have paid attention in physics class.

Thanks!

Richard

Thanks.

[orion242]

You need to work with gravity...

The sensor will have to be mounted to the bottom of the tank, and the weight of the water on one port of the sensor and atmosphere to the other.  Typically a it would be installed with a tap on the bottom (or through the side) of the tank.

Another way I have seen it done is with the sensor on the top and a tube ran down to the bottom as you describe.  Then an aquarium air pump is used to pressurize this tube.  The more water in the tank the higher the pressure will be for the air pump to push the water out.  I would assume the readings would bounce all over as the bubbles escape, but with filtering it will work.

And a third way is to use an ultrasonic mounted at the top and measure down to the surface of the water and calculate the amount of water from that measurement.

[rthorntn]

Thanks orion242!

[chibiace]

those top mounted ultrasonic sensors work alright. but they dont like foam as it gives a false reading.

[nowlan]

Here is the Washing Machine application note. Link
This would be the cheapest way short of a pure level float, etc.

Orion's method is called bubbler, and is uses the back pressure on bubbles to sense the water height.
Its best for dirty slurry which would foul sensors.
Really good video explanation.

[Zero999]

According to the datasheet, it only works with dry air.
http://www.freescale.com/files/sensors/doc/data_sheet/MPX5010.pdf

If the pipe is well sealed, you could fill the pipe with air and put the sensor at one end, above the tank and leave the other end of the pipe in the water. The air in the pipe will become compressed by the water pressure.

[orion242]

According to the datasheet, it only works with dry air.
http://www.freescale.com/files/sensors/doc/data_sheet/MPX5010.pdf

If the pipe is well sealed, you could fill the pipe with air and put the sensor at one end, above the tank and leave the other end of the pipe in the water. The air in the pipe will become compressed by the water pressure.

The problem with this is the oxygen will dissolve in the water and the volume of air in the tube will change over time.

[Zero999]

The problem with this is the oxygen will dissolve in the water and the volume of air in the tube will change over time.

That doesn't matter, the pressure inside the tube will remain proportional to the water depth. If a tiny amount of oxygen gets dissolved, it's because the pressure is higher.

[orion242]

More than a little will dissolve.  Co2 also dissolves in water, not sure about the other gases.  This action can destroy hydronic systems by rusting them from the inside out if the dissolved oxygen is not kept minimal.

If water creeps up the tube because the of this, how are you going to handle the water level in the tank going below the level in the tube putting it in a vacuum?

[Alexei.Polkhanov]

One of the most reliable level sensors I used was based on radiation absorption. You mount source of radiation at the bottom and have a sensor (basically Geiger counter) at the top of the tank. It works with foam, dirt, liquids like water, materials like cement, sugar or anything else. Only problem is that you have to re-calibrate it every year since weak radiation source tend to decay. Cs-137 usually used as radiation source. These sensors widely used in chemical industry where tanks are often filled with all sort of stuff like ceramic catalytic tubes, cubes, spheres etc.
Here they have nice overview of those sensors (bottom of page) http://www.omega.ca/literature/transactions/volume4/T9904-14-RAD.html

[orion242]

Omega love that that place.

Put in a good order and they send several hard bound books on temp, humidity, level, etc, etc theory and reference for free.

Doubt anything from them is going to be fitting in the hobbyist budget though.
 

[Kjelt]

Orion's method is called bubbler, and is uses the back pressure on bubbles to sense the water height.
Its best for dirty slurry which would foul sensors.
Really good video explanation.  

That was quite interesting, who knew we started engineering at that early age already 

[Zero999]

More than a little will dissolve.  Co2 also dissolves in water, not sure about the other gases.  This action can destroy hydronic systems by rusting them from the inside out if the dissolved oxygen is not kept minimal.

If water creeps up the tube because the of this, how are you going to handle the water level in the tank going below the level in the tube putting it in a vacuum?

At what sort of pressures are you talking about?

How about partly filling the tube with oil?