What is a relay?
Relay is a kind of controller which can turn on and turn off circuit automaticcally.
When the input parameters (such as electricity, magnetism, light, heat, sound, etc.) reach a certain value, the output parameters would change by leaps and bounds, as that to achieve the purposes of control, protection, regulation and information transmission.
Relay is one of the important components of automatic control system, remote control system and communication system.