At the heart of modern electrical engineering are the two main elements of most circuits - a semiconductor transistor and an electromagnetic relay. If you mentally remove these two inventions, it is difficult to imagine how the future history of mankind would have developed.
Perhaps there would be evolving Middle Ages around, or, perhaps, on the contrary, progress would go along the path of controlled development of
biological systems. But let’s leave these thoughts to science fiction writers. One thing is clear: the electromagnetic relay for all electrical engineering is the same as the internal combustion engine for modern vehicles. That is - an indispensable component.
How is an electromagnetic relay arranged?
The design of this circuit element is very simple. This explains its high reliability: in some industries, relays of 1940 are still in operation.
Before describing the design, it is necessary to recall one of the laws of physics - electromagnetism. It is known that around any material through which electric current passes, there is a special kind of matter - a magnetic field. Its tension (potential) depends on two parameters: the magnitude of the flowing current and the length of the conductor.
This is obvious: if each unit of length generates a field, then the longer the conductor, the more pronounced the magnetic effect. This means that if a metal object is placed next to such a conductor, then
attractive forces will influence it
. If their size is sufficient, then the object will move. Another thing is also obvious: increasing the field intensity by increasing the length of the conductor is not very convenient - the device should be compact, and the total field vector should be concentrated at one point, and not sprayed along the entire conductive material. The increase in current is also irrational, as this causes excessive heating and suboptimal use of materials. However, there is a solution.
It consists in using not a straight wire, but a coil with a core. This allows you to use kilometers of thin wire on a small volume.
The electromagnetic relay just contains such a coil inside. The second part of the design is a metal plate of a special shape, having one degree of freedom. That is, when a magnetic field occurs , the plate is attracted to the end side of the coil. When the current disappears, the action ceases, and the return spring throws the plate back to its original position.
Jumpers are fixed on the attracting bar - a group of movable contacts. The second part (rigidly fixed) is nearby. When the plate moves, the contacts close. If they are included in the open circuit, then, controlling the operation of the coil, you can commute the connected circuit. This is how the electromagnetic relay works. By the way, depending on the way the fixed contacts are arranged, they can be normally closed (open when a magnetic field appears) and normally open (assemble a circuit).
The electromagnetic alternating current relay in the design contains a special coil of the conductor, the field of which prevents rattling due to the frequency nature of such a current.