The working principle of the relay is similar, all control the opening and closing of the contact point. A relay is an electrical control device, which is an electrical appliance that makes a predetermined step change of the controlled quantity in the electrical output circuit when the change of the input quantity meets the specified requirements. It has the interactive relationship between the control system and the controlled system. 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.

The 24-volt DC relay consists of a coil, an iron core and several groups of normally open and normally closed electric shocks. When the relay coil is connected to the DC power of the rated voltage, the coil generates a magnetic field, attracting the iron core to act, the normally open contact connected to the iron core is closed, and at the same time, the normally closed contact is disconnected.

When the relay coil is powered off, the coil loses its magnetic field, the attracted iron core returns to its original position under the action of the spring, the normally open contact connected to the iron core is disconnected, and at the same time, the normally closed contact is closed.