What is a relay? A relay is an electrical control device that has an interaction between a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in automatic control circuits. It is actually a control circuit using small current to control the operation of large current "automatic switch". Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.
Its working principle is to use the interactive relationship between the relay control system and the controlled system. When the input reaches the specified value, the relay makes the controlled output circuit on or off to achieve control. The input quantity here can be divided into electric (current, voltage, frequency, power, etc.) and non-electric (temperature, pressure, velocity, etc.).