A relay is an electronic control device that has a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in an automatic control circuit. It actually uses a small current to control the larger. An "automatic switch" of current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.
1. Working principle and characteristics of electromagnetic relay
Electromagnetic relays are generally composed of a core, a coil, an armature, a contact spring, and the like. As long as a certain voltage is applied to both ends of the coil, a certain current flows in the coil, thereby generating an electromagnetic effect, and the armature will absorb the pulling force of the return spring against the iron core under the action of the electromagnetic force attraction, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position in the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are attracted. In this way, the suction and release are achieved, thereby achieving the purpose of turning on and off in the circuit. For the "normally open, normally closed" contacts of the relay, it can be distinguished as follows: a static contact that is in an open state when the relay coil is not energized, called a "normally open contact"; a static contact that is in an on state It is a "normally closed contact".
2. Working principle and characteristics of solid state relay (SSR)
The solid state relay is a kind of four-terminal device with two terminals as the input terminals and the other two terminals as the output terminals. The isolation device is used to realize the electrical isolation of the input and output.
Solid state relays can be classified 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, and the photoelectric isolation type is the most.