A relay is an electrical control device that is an electrical device that causes a predetermined step change in the controlled output quantity in the electrical output circuit when the change in the input amount (excitation amount) reaches the specified requirement. It has an interaction between the control system (also known as the input loop) and the controlled system (also known as the output loop). Often used in automated control circuits, it is actually an "automatic switch" that uses small currents to control large current operation. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.
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