The working principle of electromagnetic relay is that when the electromagnet is energized, the armature is sucked down to make the two contacts, and the working circuit is closed. When the electromagnet loses its magnetism, the spring pulls the armature up, cutting off the working circuit. It is usually used in automatic control circuits. It is actually an automatic switch that uses a smaller current to control a larger current, so it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.