The relay was the first component to be used to perform logic functions.
A simple relay consists of a coil wound around a ferromagnetic core and a metal sheet that moves between two points. It is held in place at one end by a spring and is free at the other. When an electric current is passed through the coil, it generates a magnetic field that attracts the sheet to the free end.
This breaks the circuit (switch closed). If there is no current, the sheet does not make contact at the free end (switch open). These electromechanical components were also used in former telephone exchanges.
Several variations on this mechanism are still used in control systems today.
En ausencia de esta corriente, la lámina no hace contacto por el extremo libre (interruptor abierto).
Estos componentes electromecánicos también se utilizaban en las antiguas centrales telefónicas.
En la actualidad, distintas variantes del mecanismo descrito se siguen utilizando en sistemas de control.