When the input quantity (such as voltage, current, temperature, etc.) reaches the specified value, it causes the controlled output circuit to conduct or disconnect. It can be divided into two categories: electrical quantity (such as current, voltage, frequency, power, etc.) relays and non electrical quantity (such as temperature, pressure, speed, etc.) relays. It has the advantages of fast action, stable operation, long service life, and small size. Widely used in devices such as power protection, automation, motion, remote control, measurement, and communication.

A relay is an electronic control device that has a control system (also known as an input circuit) and a controlled system (also known as an output circuit). It is commonly used in automatic control circuits and is actually an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays a role in automatic regulation, safety protection, and circuit conversion in the circuit.

Relays have been widely used in computer peripheral interface devices, constant temperature systems, temperature control, electric furnace heating control, motor control, CNC machinery, remote control systems, and industrial automation devices; Signal lights, dimming, flashing lights, lighting stage lighting control system; Instruments and meters, medical equipment, photocopiers, automatic washing machines; Automatic fire protection, security systems, as well as switching switches for power capacitors as compensation for grid power factors, etc., are widely used in explosion-proof, moisture-proof, and corrosion-resistant applications such as chemical and coal mines.