Modern electrical engineering is based on 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 further history of mankind would have developed.
Perhaps, there would have been evolved Middle Ages around, or, on the contrary, progress would have gone 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 transport. That is - an indispensable component.
How does an electromagnetic relay work?
The design of this circuit element is very simple. This explains its high reliability: some factories still operate relays from 1940.
Before describing the design, it is necessary to remember one of the laws of physics - electromagnetism. It is known that around any material through which an electric current passes, there is a special kind of matter - a magnetic field. Its strength (potential) depends on two parameters: the valuecurrent flow and conductor length.
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 it will be influenced by attractive forces. If their value is sufficient, then the object will move. Another thing is also obvious: it is not very convenient to increase the field intensity by increasing the length of the conductor - the device should be compact, and the total field vector should be concentrated at one point, and not sprayed along the entire conductive material. Increasing the current is also irrational, as it 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 kilometers of thin wire to be used in a small volume.
The electromagnetic relay just contains such a coil inside. The second part of the structure is a special-shaped metal plate with one degree of freedom. That is, when a magnetic field arises, the plate is attracted to the end side of the coil. When the current disappears, the action stops, and the return spring throws the plate back to its original position.
Jumpers - a group of movable contacts - are fixed on the attracting bar. The second part of them (rigidly fixed) is nearby. When the plate moves, the contacts close. If ato include them in a circuit break, then by controlling the operation of the coil, you can switch the connected circuits. This is how an electromagnetic relay works. By the way, depending on the way the fixed contacts are located, they can be normally closed (open when a magnetic field appears) and normally open (collect a circuit).
An electromagnetic alternating current relay in the design contains a special coil of conductor, the field of which prevents rattling due to the frequency nature of such a current.
