A relay is an electrically operated switch. It is usually used in automatic control circuits and plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. The relay consists of a set of input terminals for single or multiple control signals and a set of operating contact terminals. The switch may have any number of contacts in various contact forms, such as make contacts, break contacts or combinations thereof. Relays are used where circuits need to be controlled by independent low-power signals, or where multiple circuits must be controlled by one signal.