Electromagnetic relays are generally composed of iron core, coil, armature, contact reed, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, which will produce electromagnetic effects. Under the action of electromagnetic force, the armature will overcome the pull force of the return spring and attract to the core, thereby driving the armature. The moving contact and the static magnetic latching relay contact (normally open contact) are pulled together. When the coil is de-energized, the electromagnetic attraction will disappear, 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 pulls in and releases, so as to achieve the purpose of conducting and cutting off in the circuit. The "normally open and normally closed" contacts of the relay can be distinguished as follows: the static contact that is in the off state when the relay coil is not energized is called "normally open contact"; the static contact that is in the on state is called It is "normally closed contact".

The thermal reed relay is a new type of thermal switch that uses thermal magnetic materials to detect and control temperature. It consists of a temperature-sensitive magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting piece, a plastic substrate and some other accessories. The thermal reed relay does not use coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch. Whether the constant magnetic ring can provide magnetic force to the reed tube is determined by the temperature control characteristics of the temperature-sensitive magnetic ring.

A solid state relay is a four-terminal device with two terminals as input and the other two terminals as output. An isolation device is used in the middle to achieve electrical isolation between input and output. Solid state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, with the photoelectric isolation type being the most.