Which is the best method to measure water lever of closed tank?

[harsgh2029]

I want to measure continuous water level in the closed, vertical-cylindrical, plastic tank of capacity 1000l (h=1.5m, d=1m) which is situated on the roof-top of my building.
The tank is placed in the open atmosphere where direct sunlight and rain are common things.
Due to the direct sunlight, the maximum temperature of the tank in the summer days can go up to 55 C.
When pump is filling the tank, water inlet rate is around 1 litter/sec which causes lots random waves inside the tank.
I want to design measuring system so that it cannot be affected by such an extreme atmosphere.
And system should be compact (i.e. without or minimum mechanical arrangements).

After searching a lot, I found only feasible way by using pressure sensor. The pressure sensor can be mounted at the bottom of the tank (outside of the tank, by drilling little hole and connecting water tube to the sensor). But here drilling the hole is something I don't prefer.
The sensor can also be mounted on the top of the tank (inside the tank, by connecting air tube that goes to the bottom of the tank) but after sometime, moisture would change the volume of the air inside the tube and calibration will be changed. This can be solved by filling buffer material like silicon grease, but it introduces the relative density concept in the pressure measurement.

The other method I found is by using ultrasonic sensor. It is most convenient method without the direct contact of water. The sensor can be mounted inside the tank. But I don't know how reliable it is in the closed tank due to echo problem and under such a strong water waves when the tank is being filled (i.e. direction of reflected sound wave cannot be same as the transmitted wave due to unstable water position).

I don't want to use mechanical system like float-load connected to some kind of potentiometer.

It is the heavy water (i.e. full of minerals) So, If I use some sort of capacitive methods, due to dry minerals attachment time to time with the sensing element, di-electric constant changes and system needs re-calibration.

Water level sensing with conductivity at discrete levels is also the easiest method, but my requirement is to measure continuous level.

So, which is the best way to measure continuous water level in such an extreme environment condition.

 

[FvM]

Many points discussed in this previous thread. https://www.edaboard.com/threads/299924/
Also did you look at the "Similar Threads" shown on the bottom of this page?

As everything has been said about ultarsonic in the previous thread, I would just add that an imersed pressure sensor (with a reference pressure capillary carried along the cable) is the industry standard solution for water level measurements if a stud at the tank bottom isn't appropriate.

The mentioned "air tube" method is another industry standard e.g. for waste water, but combined with a small pump continuously bubbling air through the tube.

 

[treez]

Also there is a company in northern Ireland which does this, its in Lurgan..called sensotech or sensortronics or something like that

 

[chuckey]

I would go with ultra sound. You can integrate the output, so the level measured is the mean over several seconds. For every wave there will be a trough!
Frank

 

[treez]

**broken link removed**

...this company has solutions for you

 

[andre_luis]

Depending on latitude you live, I consider 55oC degree should be somewhat undersized considering direct sunlight exposition.
Concerning stated question, what is the purpose of measuring precisely the tank level, once is presumable some automated mechanical or electronic closed loop control ?

Pressure sensors can solve the problem, specially because there are some cheap 3-level models ( used on wash machines ), which could provide a gauge scale.


+++

 

[permute]

You might also have some luck if you use two sensors in a Kalman filter. The natural choice for the first would be one of these pressure or similar sensors. The second sensor would either be a flow sensor, or a contact for the pump. Either is a proxy for the flow into the tank. This gives the two estimators of volume -- the first based on the noisy, but direct measurement of the fluid and the second based on the smooth, but long-term inaccurate integration of water into the tank.

Of course if you have this structure, you might forego the contact/flow sensor altogether and use the existence of high-frequency to estimate input flow.

 

[m.mokhtar]

There are commercial ultrasonic level meter, it does not touch the fluid.

 

[Externet]

This is a nice subject that appears frequently on many forums with the twist now of having a plastic tank.
Many hyper complicated, expensive, unreliable solutions are usually suggested.

----> A manometer at any point in the dwelling piping can tell the level in the roof tank.

The far preferred methods like washer machine air hose, pulley and plomb... can be also unusual :

- A magnet made to float on the water surface can ride an external metal marker roller outside the tank. :-?
- If the tank is translucent; turning on a light inside could show the level from outside.