Together with the switches and switches put in action by effort of a hand in radio electronics electromagnetic relays widely are used. The relay is the device which automatically switches electrical circuits on a signal from the external environment.
In other words the relay is the device which is necessary for implementation of spasmodic changes of a condition of an electrical circuit as a result of the set entrance influences. Initially the term "relay" was applied to electromagnetic relays which were used for of strengthening of the electric cable signals weakened in extended lines of transfers to the values demanded for operation of telegraphs. The electromagnetic relay consists of an electromagnet and one or several contact groups which are run by the driving mechanism connected with an electromagnet anchor. The principle of operation of the relay is based on action of the electromagnetic forces arising in the metal core when passing current on rounds of its coil. Over the core of an electromagnet there is a mobile anchor (plate) with contacts opposite to which motionless contacts are located. Initially the anchor is kept by a spring. At emergence of tension the electromagnet attracts an anchor and closes or disconnects contacts. After the external signal stops the action, contacts return to a starting position, i.e. at contacts of the relay two operating positions – closed and opened. The electromagnetic relay is a universal switchboard of analog and pulse signals. It performs a number of the major functions. The relay is a galvanic outcome between the control circuit and a chain of loading. Thanks to the relay the operating signal breeds on several output signals, this device allows to strengthen the power of the operating signal. The relay gives the chance to operate independently several output chains with different levels of current and tension, to divide chains with various levels of working currents and tension and also chains of direct and alternating current. Thanks to the electromagnetic relay possible transformation and rationing of levels of electric signals.