1—铁芯；2—线圈；3—可动舌片；
4—弹簧；5—可动触点桥；6—静触点：
7—调整把手；8—刻度盘
When an alternating current passes through the coil 2, a magnetic flux is generated in the coil 1, which generates an electromagnetic attracting rotational torque on the movable tongue 3 to rotate it clockwise. But spring 4 produces a counteracting spring force that keeps it in position. As the current flowing through the coil increases, so does the torque that causes the tongue to rotate.
When the current flowing through the relay reaches the setting value, the electromagnetic rotation moment is enough to overcome the acting moment of spring 4, so the movable tongue 3 rotates clockwise. At this time, the movable contact bridge 5, which is located on the same rotating shaft with the movable tongue piece 3, also rotates clockwise and is connected with the static contact 6, and the relay moves.
When the current decreases, the electromagnetic rotation torque decreases. Under the action of the reaction torque of spring 4, the movable tongue 3 rotates counterclockwise, so the movable contact bridge is separated from the static contact 6, and the relay returns to its original state from the operation state to the inactive state.
