What is the function and principle of the relay? What are the functions of safety relays?

Update:22-03-2023
The function of the relay: it can increase the function range of the whole circuit, so as to achieve the purpose of controlling the high-power circuit, so that it can start automatically. Relay principle: When the input quantity is at a fixed value, the working state is changed to avoid accidents.
The functions of the safety relay are as follows: protect electrical equipment from overload, short circuit and phase loss; prevent sudden load changes in the line; protect electrical equipment from voltage fluctuations; Occurrence of dangerous phenomena such as overvoltage and undervoltage.
In order to achieve correctness and low malfunction, a variety of safety relays are produced to protect different levels of machinery, so as to reduce the possibility of errors and failures, and improve safety factors to protect machinery operators who face different levels of danger. The function of the safety relay is naturally to ensure stability and reliability. It can prevent electric shock from hurting people, and prevent dangerous situations such as circuit overload and overheating. The solid-state relay is a four-terminal device, with two terminals connected as input terminals and the other two terminals connected as output terminals. The input circuit and output circuit are electrically isolated by the isolation device. The relay is a common electrical appliance. It has the functions of automatic power adjustment and automatic protection. I hope that everyone can use the relay correctly and rationally, so as to make the indoor electricity consumption more stable.