1. Electromagnetic typeFinder relayWorking principle and characteristics of

Electromagnetic finder relay is generally composed of iron core, coil, armature, contact spring, etc. as long as a certain voltage is applied at both ends of the coil, a certain amount of current will flow through the coil, resulting in electromagnetic effect. Under the attraction of electromagnetic force, the armature will overcome the tension of the return spring and attract to the iron core, thus driving the moving contact and the static contact (normally open contact) of the armature to attract. When the coil is powered off, the electromagnetic attraction will also disappear, and the armature will return to its original position under the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) will be attracted. The normally open contact and normally closed contact of finder relay can be distinguished as follows: the static contact in the disconnected state when the coil of finder relay is not energized is called normally open contact, and the static contact in the connected state is called normally closed contact.

2. Working principle and characteristics of thermal dry spring relay

Thermal dry spring relay is a new type of thermal switch which uses thermal magnetic materials to test and control temperature. The utility model is composed of a temperature sensing magnetic ring, a constant magnetic ring, a clarinet, a heat conducting mounting piece, a plastic lining plate and other accessories. The thermal dry spring relay does not use coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch action. Whether the constant magnetic ring can provide magnetic force to the clarinet is determined by the temperature control characteristics of the temperature sensing magnetic ring.

3. Working principle and characteristics of solid state relay (SSR)

Solid state relay is a four terminal device with two terminals as input terminals and two terminals as output terminals. An isolation device is used in the middle to realize the electrical isolation of input and output.

Solid state relay can be divided into AC type and DC type according to the type of load power supply. According to the type of switch, 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 photoelectric isolation type as the majority.