The coil of a relay is represented by a rectangular symbol in the circuit. If the relay has two coils, two rectangular symbols are drawn side by side.
The relay’s letter symbol “J” is marked inside or next to the rectangular symbol. There are two ways to represent the contacts of a relay: one way is to draw them directly on one side of the rectangular box, which is more intuitive.
The other way is to draw each contact in its respective control circuit according to the circuit connection needs.
Usually, the same letter symbol is labeled next to the contacts and coil of the same relay, and the contacts are numbered to distinguish them.
There are three basic forms of relay contacts:
1. Normally Closed (NC) contact: When the coil is not energized, the contact is closed; when the coil is energized, the contact opens.It is represented by the letter “D” for “断” (disconnected).
2. Normally Open (NO) contact: When the coil is not energized, the contact is open; when the coil is energized, the contact closes. It is represented by the letter “H” for “合” (connected).
3. Changeover (CO) contact: This is a group of contacts. This contact group consists of three contacts: one is the moving contact in the middle, and one static contact is above and below. When the coil is not energized, the moving contact is disconnected from one static contact and connected to the other. When the coil is energized, the moving contact moves to change the state, and the originally disconnected contact closes while the originally closed contact opens, achieving the purpose of switching. Such a contact group is called a changeover contact and is represented by the letter “Z” for “转” (change).
Post time: Jun-26-2023