Generally speaking, the relay is composed of two parts: the contact and the coil, so the graphic symbols in the relay circuit diagram also include two parts: a group of contact symbols represents the contact combination; and a rectangular box represents the coil; when the contacts are not many and the circuit is relatively simple, the contact group is often directly drawn on the side of the coil frame, which is generally called set Chinese representation. Simple and clear, easy to understand.
When a relay has two coils, two parallel rectangular frames are usually drawn. Generally, the text symbol of relay [J] is marked beside the rectangular box or at the appropriate position of the rectangular box. There are generally two ways to express the contacts of relays: one is to draw them directly on the side of the rectangular frame, which is more intuitive; the other is to draw each contact into its own controlled circuit according to the requirements of circuit connection, and mark the same text symbol beside the contact and coil of the same relay, and mark the contact points Group codes are also numbered to achieve their own differences.
The contact of relay usually has three basic forms, as follows:
1、 Dynamic break type [normally closed] [D type]
When the coil is not energized, the two contacts are closed, and the two contacts are disconnected after power on. It is usually represented by the phonetic prefix [D] of a broken character.
2、 Dynamic closing type [normally open] [H type]
When the coil is not energized, the two contacts are disconnected, and the two contacts are closed after power on. It is usually represented by the phonetic prefix [H] of a compound character.
3、 Conversion type [Z type] contact group type
Generally, such a contact group relay has three contacts in total: the middle is the moving contact, and the upper and lower static contacts. When the coil is not electrified, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is electrified, the moving contact moves to make the original open into closed state and the original closed to open state, so as to achieve the effect of conversion. Such a contact group is called a change-over contact. It is represented by the phonetic prefix [Z].