A relay , also known in some countries as relay or relay , is a switch whose control is the responsibility of an electrical circuit. Developed in the first half of the XIX century by the American physicist Joseph Henry , through a coil and a electromagnet It affects various contacts for opening or closing other circuits, which operate independently.
What does the coil is to create a magnetic field that leads contacts to establish a connection. He electromagnet , for its part, allows the closure of contacts. In this way, the relay acts as a switch that can encourage the passage of electric current or its interruption.
The relays, in short, allow to develop a remote commutation, controlling high voltages with a low return voltage. They also serve to interrupt the AC power supply. The cars and the telephonic central For example, they have relays.
In simpler words, the relay allows you to control a large number of electricity operating with a very small amount. These are instruments that provide greater security in different devices that work with the use of electrical energy, since their contacts allow to open or close electrical circuits (that is, generate or interrupt the connection).
According to what delays the deactivation and activation, the intensity which tolerate and the number of contacts, it is possible to classify the relays in different ways, as can be seen below.
Electromechanical relay
This, in turn, is divided into several types:
* armor type : It is the oldest, but this does not mean that it is also the most used in a large number of applications. It consists of an electromagnet which, when excited, generates the tilting of an armor, through the closing or opening of the contacts as normally closed (N.C.) or normally open (N.A.);
* mobile core : where the former has an armor, it has a plunger. Since it has a greater force of attraction, it becomes necessary to use a physical device known as solenoid To close the contacts. The solenoid can generate a countryside extremely intense magnetic and of great uniformity in its interior, and with little intensity in its exterior;
* tongue : also known as reed, and consists of a glass ampoule that has within it a series of contacts arranged on thin metal sheets.
Solid state relay
It's about a circuit hybrid that is usually formed by a device such as the triac, which serves to interrupt the power, a trigger circuit, which is responsible for detecting the passage of the line current through zero, and a optocoupler, for the isolation of the entrance.
The origin of its name is that it resembles an electromechanical one and its most common applications involve the constant use of contacts that would wear a conventional relay too much, and the switching of high amperages that could destroy contacts of an electromechanical relay in a very short time.
AC relay
By exciting the coil of a relay with alternating current, the magnetic flux also becomes alternate and this produces a force on the pulsating and double-type contacts frequency . In some parts of the world, such as Latin America and certain European countries, the contacts of a relay connected to a network oscillate at 2 x 50 Hz, while in North America they do so at 2 x 60 Hz (something that is used as the basis of buzzers and bells); An AC relay has the mission of modifying the resonance to avoid such oscillation.
