pressure level sensor problem


Thread Starter


I want to know the exactly volume of a liquid in a tank that is not sealed, so what I do is measure the liquid level using a pressure sensor and with an algorithm determine the volume. I use a differential pressure sensor from Motorola (with an amplifier), I connect positive port to the top of a pipe and seal between pipe and port sensor to avoid a leak of air, the other port is to pressure atmosphere. Then I introduce the bottom side of the pipe in the tank and it gives me the right data corresponding to the level.

The problem is when tank start to move and create waves inside, the liquid start to move too much and the problem is that the air inside the pipe leaves in form of bubble, the liquid enters the pipe and my system stop to be calibrated. :S So I don’t know what to do to solve my problem any other method using the same sensor?
Please help me! :(

Koblenz, Mykel MH

if your tank is as you say not sealed ie the airspace is a atmospheric pressure then you do not need to use a differential pressure transmitter. A pressure transmitter measuing the pressure at the bottom (or near bottom) of
the tank will suffice. You should not have to have an impulse line to the vapour space of tha tank.

Correct me if I am wrong in understanding your requirements.


Robert Scott

Instead of trying to maintain liquid in the pipe to the positive port, use a bubbler to ensure that the positive port has only air. A steady stream of bubbles will emerge from the pipe at the bottom of the tank. The bubbler pump input can be from the air at the top of the tank rather than from ambient air to ensure a closed system. Then just measure the differential pressure between the bubbler output and the air at the top of the tank.

-Robert Scott
Real-Time Specialties
Embedded Systems Consulting

Dan Karppi, (SudburySmelter\)

How large is the tank that you are trying to measure the level in. What are the dimensions of the tank. When you say the tank starts to move around, it makes me think that the tank is small. Can you give us more details such as tank size, tank shape, what kind of liquid is it, is the liquid corrosive, what is the temperature of the liquid, are there vapours present etc.

i want to know more about bubblers i undestend the concept but where can i get info about. in order to see how can i interconect in my system.
Hi Dan the liquid im trying to mesure is automotive diesel. the tank is an orizontal cylindrical type, about 60cm x 280cm what do you think about bubblers?
thanks Mick your idea is good. the problem is installation. (tank must be empty) and that complicate things. any other ideas?
A bubbler could work but it would need a source of clean dry compressed air. To learn more about liquid level measurement using a bubbler system have a look at this web page. This site also explains other level measurement techniques as well.

As far as using the pressure sensor that you already have, I can only suggest installing a restriction orifice at the bottom of the tube that you are using for the high pressure side of the transducer. The restriction orifice would delay the flow of fuel into your measurement tube and tend to stabilize your measurement. This probably can only be done with an emptied tank.

Another way that might work without draining the tank is to attach your sensor port to a second tube that would be inserted into the existing tube. This tube can be pinched off at the end and then a hole drilled into it to provide you with a restriction orifice. Start with a hole about 1mm and make it larger if you need to.

If this doesn't work well enough you may have to use another type of level measurement sensor. A sensor that can be installed without draining the tank is a resistive tape level sensor. You can learn more about this device at this web site.
I want to ask a question. I am doing a project entitled Closed Tank Pressure Monitoring using Computer. My problem is I don't know how to implement the pressure sensor in the closed tank. Can someone explain to me the operation? my email [email protected]