Electromagnetic relay is an electronic control device that has a control system (also known as input circuit) and a controlled system (also known as output circuit). It is usually used in automatic control circuits. It is actually an "automatic switch" that uses smaller currents and lower voltages to control larger currents and higher voltages. Therefore, it plays a role in automatic regulation, safety protection, and conversion circuits in the circuit. Electromagnetic relays are widely used in fields such as aviation, aerospace, shipbuilding, and home appliances, mainly completing functions such as signal transmission, execution control, and system power distribution. They are one of the key electronic components in various systems. Electromagnetic relay is a switch that uses an electromagnet to control the on-off of the working circuit (1) Structure: The main components of an electromagnetic relay are electromagnet A, armature B, spring C, moving contact D, and static contact E (2) The working circuit can be divided into two parts: a low-voltage control circuit and a high-voltage working circuit. The low-voltage control circuit includes an electromagnetic relay coil (electromagnet A), a low-voltage power supply E1, and a switch S; The high-voltage working circuit includes the high-voltage power supply E2, the motor M, and the contacts D and E of the electromagnetic relay (3) Working principle - Close the switch S in the low-voltage control circuit, and the current flows through the coil of electromagnet A to generate a magnetic field, which generates a gravitational force on armature B, causing the dynamic and static contacts D to come into contact with E. The working circuit is closed, and the motor operates; When the low-voltage switch S is disconnected, the current in the coil disappears. Under the action of spring C, the armature B disengages the dynamic and static contacts D and E, causing the working circuit to disconnect and the motor to stop working. As long as a certain voltage is applied to both ends of the coil, a certain amount of current will flow through the coil, generating electromagnetic effects. The armature will overcome the pulling force of the return spring and attract it towards the iron core under the attraction of electromagnetic force, This drives the dynamic contact of the armature to engage with the static contact (normally open contact). When the coil is powered off, the electromagnetic attraction also disappears, and the armature will return to its original position under the reaction force of the spring, releasing the moving contact and the original static contact (normally closed contact). This suction and release achieves the purpose of conduction and disconnection in the circuit. For the "normally open and normally closed" contacts of relays, they can be distinguished as follows: the static contacts that are in the disconnected state when the relay coil is not energized are called "normally open contacts"; The static contact in the on state is called a "normally closed contact"