1. Relay, also known as electric relay, is an electronic control device. It has a control system (also known as input circuit) and a controlled system (also known as output circuit). It is usually used in automatic control circuits. The above is an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.

2. The relay coil is represented by a long box symbol in the circuit. If the relay has two coils, draw two parallel long boxes. At the same time, mark the relay's text symbol "J" in or beside the long box.
3. Because the relay is composed of two parts, the coil and the contact group, the graphic symbol of the relay in the circuit diagram also includes two parts: a long box represents the coil; a group of contact symbols represents the contact combination. When there are not many contacts and the circuit is relatively simple, the contact group is often drawn directly on one side of the coil frame, which is called centralized representation.