Relay, also known as Relay, is an electronic control device. It has control system (also known as input loop) and controlled system (also known as output loop). It is usually used in automatic control circuit. Therefore in the circuit plays the role of automatic regulation, safety protection, conversion circuit. Relay coils are represented by a long box symbol in the circuit. If the relay has two coils, draw two parallel long boxes. At the same time in the long box or the long box next to the text symbol "J" relay. There are two ways to represent the contact of the relay: one is to draw them directly to the side of the long box, which is more intuitive.