What is a relay

Relay (English name: relay) is an electrical control device, which is an electrical appliance that causes a predetermined step change in the controlled quantity in the electrical output circuit when the change of input quantity (excitation quantity) meets the specified requirements. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in automated control circuits, it is actually a kind of "automatic switch" that uses small current to control large current operation. Therefore, it plays the role of automatic adjustment, safety protection, conversion circuit and so on in the circuit.