A relay is an electrically operated switch that opens and closes circuits by receiving electrical signals from outside sources. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms. Relays are useful in many applications where it is necessary to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable. They are also used as auxiliary relays in the contact systems of protective relay schemes, for differential protection and the over- or under-current protection of various AC and DC equipment.
Relays can be used for a wide range of applications such as home automation, cars and bikes (automobiles), industrial applications, DIY Projects, test and measurement equipment, and many more. They can be used in either an AC circuit or a DC circuit. AC relays are constructed with a special mechanism such that continuous magnetism is provided in order to avoid the problem of continuous breaking of the circuit.
The principle of relay logic is based on relays which energize and de-energize associated contacts. A number of relays could be used together to carry out complex functions. Relays were the standard method of controlling industrial electronic systems for many years.
In summary, a relay is an electrically operated switch that can be used to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable. They can be used for a wide range of applications and can be constructed for either an AC or DC circuit.
