Electrical symbol and contact form of the relay
The relay coil is represented by a long box symbol in the circuit. If the relay has two coils, the two parallel long boxes are drawn. At the same time, mark the text symbol "J" in the relay box or next to the long box. There are two ways to represent the relay contacts: one is to draw them directly on the side of the long box, which is more intuitive. The other is according to meet the needs of the circuit connection, each contact into their own control circuit, usually on the contact and coil of the same relay, and the contact group on the number to show the difference. Relay contacts come in three basic forms:
1. When the dynamic composite type (H type) coil is not electrified, the two contacts are disconnected. After electrification, the two contacts are closed. It is indicated by the pinyin prefix "H".
2. When the broken type (type D) coil is not electrified, the two contacts are closed after electrification. Use the broken word pinyin prefix "D".
3. Conversion type (type Z type) This is the contact group type. This group of contacts has three contacts, namely one in the middle, and one static contact up and down. When the coil is not energized, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is electrified, the moving contact will move, so that the original disconnected state is closed, and the original closed disconnected state is closed to achieve the purpose of conversion. Such a group of contacts is called the transition contacts. Use the pinyin prefix "z" of the word "turn".
Selection of relays
1. First understand the necessary conditions: ① control circuit supply voltage, can provide the maximum current; ② voltage and current in the controlled circuit; ③ control circuit needs several groups, what form of contacts. When selecting the relay, the power supply voltage of the general control circuit can be used as the basis for the selection. The control circuit shall provide sufficient working current to the relay, otherwise the relay suction is unstable.
2. After consulting the relevant information to determine the conditions of use, you can find the relevant information to find out the model and specification number of the relay. If you have a relay on hand, check whether it can be used according to the data. Finally, consider whether the size is appropriate.
3. Pay attention to the volume of the appliance. If used for general electrical appliances, in addition to considering the volume of the chassis, small relays mainly consider the circuit board installation layout. For small electrical appliances, such as toys, remote control devices should choose ultra-small relay products.
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