Relays are made up of two main components: the coil and the contact set. In circuit diagrams, the graphical representation of a relay also consists of these two parts. A long rectangle is used to represent the coil, while a set of contact symbols shows the contact configuration. When the circuit is simple, the contacts are often drawn directly next to the coil symbol. This method is known as centralized representation.
Electrical symbols and contact types:
The coil of a relay is shown as a long rectangle in the diagram. If a relay has two coils, two separate rectangles are drawn. The text symbol “J†is usually placed inside or near the coil symbol. As for the contacts, there are two common ways to represent them. One is to draw them directly next to the coil, which makes the diagram more intuitive. The other is to place the contacts in their respective control circuits depending on the needs of the overall design. Typically, the same text symbol is used for both the coil and its corresponding contacts, and each contact group is labeled with a number to distinguish them clearly.
There are three basic types of relay contacts:
1. Normally open (H type): When the coil is not energized, the two contacts are open. Once the coil is activated, the contacts close. This type is represented by the pinyin initial “Hâ€.
2. Normally closed (D type): When the coil is not energized, the two contacts are closed. Upon energization, the contacts open. This is denoted by the pinyin initial “Dâ€.
3. Changeover (Z type): This contact type features three terminals—two fixed contacts and one moving contact. When the coil is inactive, the moving contact is connected to one of the fixed contacts and disconnected from the other. When the coil is energized, the moving contact shifts, switching the connection from one fixed contact to the other. This allows for a switching function between two circuits. Such a contact set is called a changeover contact and is marked with the pinyin initial “Zâ€.
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