Using float systems for level measurement
Measuring the position of a float on the surface of a liquid by means of a suitable transducer is another fairly simple and cheap method of liquid level measurement. The system using a potentiometer is very common, and is well known for its application to monitoring the level in motor vehicle fuel tanks.
An alternative system, which is used in greater numbers, is called the float and tape gauge (or tank gauge). This has a tape attached to the float which passes round a pulley situated vertically above the float. The other end of the tape is attached to either a counterweight or a negative-rate counterspring. The amount of rotation of the pulley, measured by either a synchro or a potentiometer, is then proportional to the liquid level.
These two essentially mechanical systems of measurement can achieve quite high levels of accuracy, but their maintenance requirements are always high.