# Physics homework – Float switch for level monitoring

In all German states, it is customary to discuss the topic of electricity in physics lessons. There, the pupils learn how electricity works, how magnetic fields, current strength and voltage strength are interdependent, etc. They also learn about resistors and capacitors. They also learn about resistors and capacitors. This topic is also extremely important, as electricity plays a major role in our modern world. Hardly anything today can do without e-technology, microchips or sensors. Every now and then, the students are given a special homework assignment.

One in which they have to come up with a solution to a problem from this subject area. But! – one where no laser or other computer can help. One of the most common tasks is to find a method for monitoring the levels in containers. In other words, a mechanism that ensures that a vessel does not overflow or fall below a certain level. How can this be achieved? The only means available are those that existed in the days of our grandfathers. How do you do it? Here is the solution for this task.

## Solution Physics homework: mechanical-electrical level measurement

Yes, it is actually possible to solve this problem, without microelectrics and computers etc. There are 2 common ways to solve the problem:

• Float switch
• Reed relay circuit

We show how both methods work.

## Solution #1: Float switch for level measurement

It is a very simple device, the float switch or float switch. It is a construction that was already used in the middle and end of the 19th century. A vessel is tied to a string or cable. This vessel is so light that it floats on the surface of the liquid. Inside is a ball of metal so that it conducts electricity. It is fixed in a rolling track in which it can move back and forth. If liquid is now let into the vessel, the switch floats on the surface. At some point, however, the string ends. This is exactly as long as the desired filling level is high. When it reaches the maximum, it comes under tensile stress and the vessel rotates. At this point, the ball rolls into another position. There it touches a contact. This in turn triggers a motor that is responsible for pumping out the liquid. You can see it here in the video:

Very simple, but incredibly clever. The advantage of this method is that it is virtually foolproof. No chips break here, so that the technology fails. It works as good as always. If the cable is stable and the rolling path of the ball is free of dirt, then such a switch works reliably like a bomb. And it will do so for years without any problems.

## Solution #2: Reed relay technology

A second variant also has something to do with swimming. However, the method by which a circuit is closed is somewhat different. A so-called reed relay is attached to a holder on the wall of the vessel, which is mounted on a kind of rail. Such a reed relay contains a copper switch in a thin glass vessel, which is not closed. Here you can see the method in the video:

In addition to the reed relay, a magnet is also attached to the holder with the rail, which has been placed in a floatable housing. This moves up and down with the level on the rail. When it reaches the height of the reed switch at some point, the magnet generates a magnetic field that causes the relay to close. From now on, current flows. This is used to drive a motor. Depending on the choice and purpose of the switch, this motor can now start pumping liquid out of the container. Or pump some in. So depending on whether the user wants to protect something from overflowing, or from there being too little liquid in a container.

## Conclusion: mechanical-electronic level measurement

Many young engineers do not know the “good old days”. You think in terms of microchips and software, you want to install smart AI cameras and sensors. But in terms of increased safety, it is sometimes more reliable and, above all, cheaper to make use of a few tried-and-tested tricks.