The relay coil is indicated by a box symbol in the circuit. If the relay has two coils, draw two juxtaposed boxes. At the same time in the rectangular box or long box marked next to the relay symbol "J". Relay contact there are two ways to express: one is to draw them directly on the side of the box, this representation is more intuitive. The other is in accordance with the needs of the circuit connection, the various contacts were drawn to the respective control circuit, usually in the same relay contacts and coils are marked with the same text symbols, and the contact group number, To show the difference. There are three basic forms of relay contacts:
1. The moving contact (H type) coil is not energized, the two contacts are disconnected, after power, the two contacts closed. To pinyin pinyin prefix "H" said.
2. Momentary off (D type) When the coil is not energized, the two contacts are closed, the two contacts after the power is off. Use hyphenated pinyin prefix "D".
3. Conversion type (Z type) This is the contact type. This contact group has a total of three contacts, that is, the middle of the moving contacts, each up and down a static contact. When the coil is not energized, the movable contact and one of the stationary contacts are disconnected and the other is closed. After the coil is energized, the movable contact moves so that the original switch is closed and the original switch is turned off to reach the switched purpose. Such a contact group is called a changeover contact. Use "turn" word pinyin "z" said.