Inside a tank the usual method is to measure the depth of the liquid. Then knowing this and the cross sectional design of the tank it is a relatively straight forward task to compute liquid volume in the tank.

There are probably as many ways to measure the liquid level in a tank as there are engineers to work on the problem. One of cleverest simple schemes I ever heard about was one that measured not the liquid depth but instead measured the distance from the tank opening to the top of the liquid thus actually measuring the degree of tank emptyness. That system was made for huge tanks and was based upon a float that was lowered down to the liquid surface via a string and a small motor. The string was metered out and measured as counts of steps of the motor or some encoder scheme. The surface detection used some type of tension measuring system on the pull of the string.

One could even envision a similar system wherein a float switch on a two conductor wire was lowered down till the switch closure was detected. Distance could be determined by how long it took to lower the float switch provided you spooled the wire out slowly and at a consistent rate. (i.e. d = v * t)


Michael Karas