1. The working principle and characteristics of electromagnetic relays

Electromagnetic relays are generally composed of an iron core, coil, armature, contact spring, etc. As long as voltage is applied to both ends of the coil, a current will flow through the coil, generating electromagnetic effects. The armature will overcome the pulling force of the return spring and attract the iron core under the attraction of electromagnetic force, thereby driving the moving contact of the armature to engage with the static contact (normally open contact). When the coil loses power, 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 a relay, they can be distinguished as follows: the static contacts that are in a disconnected state when the relay coil is not energized are called "normally open contacts"; The static contact in the connected state is called a "normally closed contact".

2. The working principle and characteristics of thermosensitive reed relay

Thermal reed relay is a new type of thermal switch that uses thermal sensitive magnetic materials to detect and control temperature. It consists of a temperature sensing magnetic ring, a constant magnetic ring, a reed tube, a thermal conductive mounting plate, a plastic substrate, and other accessories. The thermosensitive reed relay does not require coil excitation, but is driven by the magnetic force generated by the constant magnetic ring to operate 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 sensing magnetic ring.

3. The working principle and characteristics of solid-state relay (SSR)

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

4. Magnetic reed relay

Magnetic reed relay is a coil sensing device that uses a coil to generate a magnetic field to activate the magnetic reed tube. Therefore, the characteristics of magnetic spring relays include small size, lightweight, fast response speed, and short jump time. When a whole piece of ferromagnetic metal or other magnetic material approaches it, an action occurs to open or close the circuit. Composed of magnets and reed tubes. The magnet and reed are fixed on a bracket that is neither magnetic nor magnetic. The line connecting the north and south poles of the magnet should be the axis, which should coincide or basically coincide with the axis of the reed. Adjust the distance between the magnet and the reed pipe from far to near, and fix the position of the magnet when the reed pipe just moves (for normally open reed pipes, it becomes closed; for normally closed reed pipes, it becomes open). At this point, when a whole piece of magnetic material, such as an iron plate, approaches both the magnet and the reed, the reed will move again and return to its state without the action of a magnetic field; When the iron plate leaves, the reed tube moves in the opposite direction. The magnetic spring relay has a sturdy structure, sealed contacts, and high practicality. It can be used as a position limit switch for mechanical equipment, as well as to detect whether iron doors, windows, etc. are in designated positions.

5. Optical relay

Photorelay is a semiconductor relay used in combination with AC/DC, which refers to a device that integrates light-emitting devices and light-receiving devices. The input and output sides are electrically insulated, but signals can be transmitted through optical signals. Its characteristics include semi long lifespan, small current driving signal, high impedance insulation and voltage resistance, ultra small size, optical transmission, contactless. Mainly used in measurement equipment, communication equipment, security equipment, etc.