Tank level equation using pressure

[AshleyParr]

Hello guys,

Just looking into getting some code ready for our tank farm level project. We are installing pressure transducers at the top and bottom of the tank, i want to use the differential to calculate the volume.

I took a look around but either cant find a post relating to it or am blind.

The tank also has a cone at the bottom of the tank, have you guys found this is worth taking into account?

Cheers Ash

 

[Bit_Bucket_07]

The tank also has a cone at the bottom of the tank, have you guys found this is worth taking into account?

That depends upon how much product the conical region can hold and whether the customer considers measuring the contents of the cone to be critical to their operation.

If you can ignore the cone, consider the bottom of the cylindrical portion of the tank to be the zero point and place your pressure transducer there, then you will greatly simplify the application, since you could then directly convert the gauge pressure measured between 0 and 100% of tank fill to tank level. Of course, this assumes a vented tank, which would also render the second pressure transmitter redundant.

 

[cardosocea]

You mean this:

http://www.lmnoeng.com/Statics/pressure.php
https://www.sensorsone.com/pressure-to-liquid-level-calculator/

Do you know the density of the liquid?
If you don't, and can move your top sensor to a known distance from the bottom one, you can also calculate it by using the formulas above.

 

[danw]

I hope that the pressure transmitter is a differential pressure transmitter (DP) with two ports, a high side port and a low side port. The high side gets piped to bottom, the low side piped to the top.

Subtracting the readings from two separate pressure transmitters creates too much error.

The internal measurement technology of a DP transmitter provides a very accurate measyrement of hydrostatic head pressure.

The technology also assumes the specific gravity/density of the liquid remains constant. Any change in the SG is reflected in a pressure measurement.

 

[Paullys50]

It's really just a geometry problem. Volume of the cone + volume of a cylinder. As Bit_Bucket_07 mentioned, there is consideration for accuracy here as the tank construction could include some radius where the cone meets the cylinder, and it's probably not a true cone because the pressure sensor will be mounted on the side rather than true bottom.

So now it's a volume of a trapezoid + volume of a cylinder + volume of unmeasured (whatever is below the bottom pressure sensor). You will need dimensional drawings of the tank so you can create the equations.

Or, you could create a lookup table. Start filling a tank through a flowmeter totalize and capture measurement points along the way. Tedious, especially if tanks vary in sizes, and possibly not a realistic option if you have very large tanks.

 

[just the cowboy]

Outside or inside?

We had problems with out outside tankfarm and pressure xmiters. When the sun heated the tank convection motion would change the numbers. Also if you use mixers pressure is no good