A switch relay, commonly known simply as a relay, is an electromechanical device employed to control the operation of another circuit using a low-power signal. It comprises several essential components： an electromagnet (coil), an armature (moving contact), and one or more sets of contacts (fixed contacts). When an electric current passes through the coil, it generates a magnetic field that attracts the armature, closing the contacts and allowing current to flow through the output circuit. When the current is removed, the armature returns to its original position, opening the contacts and interrupting the current flow.