Electromagnetic relay is a commonly used in automatic control circuit components. In fact, it is an automatic switch that controls a larger current with a smaller current and is widely used in electronic equipment. Electromagnetic relay generally consists of a coil, core, a group or groups of contacts with reed components. Contacts have moving contact and static contact points, in the course of their work can be called moving contact, can not move called static contact.

The main characteristics of the relay parameters

Rated operating voltage or rated operating current: This refers to the relay operating voltage or current coil needs. The construction of one type of relay is roughly the same. In order to adapt to different voltage circuit applications, a type of relay usually has a variety of rated operating voltage or rated current, and use the standard model to be distinguished.

DC Resistance: This refers to the DC resistance of the coil. Some product specifications given in the rated voltage and DC resistance, then Ohm’s law can be determined according to the rated current. If known operating current and DC resistance, but also find the rated operating voltage.

Pull-in current: It refers to the relay can produce the minimum current pull-action. In actual use, to make the relay a reliable pull, the given voltage can be equal to or slightly higher than the rated operating voltage. Generally not greater than 1.5 times the rated operating voltage, otherwise it will burn the coil.

Release current: It refers to the relay to generate the maximum current release action. Reduce the current in the pull-in relay state, when the current decreases to a certain extent, the relay returns to the state when not powered, this process is called the relay release action. Release current is much smaller than the pull-in current.

Contact load: It refers to the voltage or current allowed by the relay contacts. It determines the relay can control the voltage and current size. Applications can not use a small contact load relay to control high current or high voltage.

Electrical symbols and contact form of relay

The relay coil is indicated by a box symbol in the circuit. If the relay has two coils, draw two juxtaposed boxes and mark the relay symbol “J” in the box or next to the box. 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 contact and next to the circle next to the same text symbol, and the contact number to be compiled , To show the difference. There are three basic forms of relay contacts:

Dynamic type (H type): When the coil is not energized, the two contacts are disconnected, and the two contacts are closed after the power is turned on. To pinyin pinyin prefix “H” said.

Momentary off (D type): the two contacts are closed when the coil is not energized, the two contacts on the power is off. Use hyphenated pinyin prefix “D”.

Conversion type (Z type): This is the contact type. This contact group 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 called the conversion contact, with the word pinyin prefix “Z” said. In addition, a relay can also have one or more contact groups, but nothing more than the above three forms. In the circuit diagram, the contact and contact group of painting, the provisions of all the time is not energized state draw.

Relay selection

The necessary conditions for the relay are the supply voltage of the control circuit, the maximum current that can be supplied, the voltage and current in the control circuit, the groups of contacts to be controlled, and the types of contacts. Selection of relays, the general control circuit current voltage can be used as a basis for selection. Control circuit should be able to provide sufficient relay current, or pull the relay is unstable. Determine the conditions of use, you can find the relevant information to find the required relay model and specification number. If you have a hand on hand, according to the data check whether it can be used.

Finally consider the size is appropriate.

In addition, you should also pay attention to the volume of the appliance. If it is used for general electrical appliances, in addition to considering the volume of the chassis, the main consideration of small relays circuit board installation layout.

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