A relay is an electrical component that uses the principle of electromagnetism to attract higher-power loads and also plays a role in isolation.

The DC relay generally uses a 5V-24V input voltage at the control end. After the voltage is applied to the control end, the internal electromagnet will be pulled in, which will drive the internal contacts to disconnect and conduct. The control terminal indicator is voltage, and the output terminal (load) indicator is voltage and current.
When the change of the input quantity (excitation quantity) reaches the specified requirements, an electrical appliance that makes a predetermined step change of the controlled quantity in the electrical output circuit.
A relay is an electrical control device. 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 an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.