On many household appliances (such as automatic washing machines, electric furnace heating, etc.), in order to prevent the electrical appliances from being damaged due to excessive current, some relays are installed on the electrical appliances. The relay is an electronic control device, which is actually an "automatic switch" that uses a smaller current to control a larger current. So how does the relay work? What are its functions? Let's take a look together:
1. Basic concepts
A relay is an electrical control device, which is an electrical appliance that causes the controlled quantity to undergo a predetermined step change in the electrical output circuit when the change of the input quantity (excitation quantity) meets the specified requirements. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in automatic control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. последовательный модуль
In the 1830s, American physicist Joseph Henry invented the relay by using the phenomenon of electromagnetic induction when studying circuit control. The earliest relay is an electromagnetic relay, which uses the phenomenon that the magnetic force of the electromagnet is generated and disappeared under power-on and power-off to control the opening and closing of another circuit with high voltage and high current. Its appearance makes the remote control and protection of the circuit work be carried out smoothly. The relay is a great invention in the history of human science and technology. It is not only the basis of electrical engineering but also an important foundation of electronic technology and microelectronic technology.
2. Circuit symbol
The text symbol of the relay is "K". In the circuit diagram, the contacts of the relay can be drawn next to the relay coil, or at a place far away from the relay coil, and their mutual relationship is indicated by numbers.
3. Main function
(1) Amplification: For example, sensitive relays, intermediate relays, etc., can control large-power circuits with a very small control amount.
(2) Integrated signal: For example, when multiple control signals are input into a multi-winding relay in a prescribed form, they will be compared and integrated to achieve the predetermined control effect.
(3) Automatic, remote control, and monitoring: For example, the relay on the automatic device, together with other electrical appliances, can form a program control circuit to realize automatic operation.
(4) Expand the control range: For example, when the control signal of the multi-contact relay reaches a certain value, it can switch, break, and connect multiple circuits at the same time according to the different forms of the contact group.
4. Basic structure
The relay consists of four parts, which are coil, magnetic circuit, reaction force spring and contact.
The purpose of the coil is that after electrification, it can generate electromagnetic attraction, drive the armature of the magnetic circuit to attract and close, and cause the contact to produce a displacement action. Беспроводной модем
The magnetic circuit is composed of iron core, iron yoke and armature, and its task is to establish a magnetic circuit channel for the magnetic flux generated by the coil.
In the magnetic circuit, the most important thing is the magnetic circuit air gap, which is a gap between the armature and the iron core. When the coil is not energized, the air gap is the maximum value, and the contacts are in the initial state; after the coil is energized, the air gap is zero, and the contacts are displaced to the action state.
The function of the reaction force spring is to provide the armature with a repulsive force opposite to the action direction. When the coil is powered off, it can help the armature and contacts to reset.
The contacts are used for external control output, which consists of normally closed contacts and normally open contacts. After the coil is energized and the relay is closed, the normally closed contact is opened and the normally open contact is closed. After the coil is powered off and released, both the normally closed contact and the normally open contact are reset to the initial state.
5. Working principle
The changeover contact of the relay is one moving contact and two static contacts of the relay. Among them, the moving contact and the static contact 1 are in a closed state, which is called a normally closed contact, and the moving contact and the static contact 2 are in a disconnected state, which is called a normally open contact.
When the coil is energized, its moving contact is immediately disconnected from the static contact 1 and closed with the static contact 2, cutting off the control circuit of the static contact 1 and contacting the control circuit of the static contact 2.
When the coil is de-energized, the moving contact is reset, that is, the moving contact is reset and disconnected from the static contact 2 and reset and closed with the static contact 1, cutting off the control circuit of the static contact 2 and connecting the control circuit of the static contact 1.
It can be seen that when the relay K coil is connected between the normally open button that is not locked and the battery; the normally closed contact K-1 is connected between the battery and the light bulb EL1z to control the lighting and extinguishing of the light bulb EL1; the normally open contact Point k-2 is connected between the battery and the light bulb EL2, and is used to control the light bulb EL2 to turn on and off. When the circuit is not connected, the light bulb EL2 is in the extinguished state.
When the button SB is pressed, the line is connected, the relay K coil is energized, the normally closed contact K-1 is disconnected, the power supply of the bulb EL1 is cut off, and the bulb EL1 is extinguished; at the same time, the normally open contact K-2 is closed, and the bulb is turned on The power supply of EL2, the light bulb EL2 lights up.
When the button SB is released, the circuit is disconnected, the coil of the relay K loses power, the normally closed contact K-1 is reset and closed, the power supply of the bulb EL1 is connected, and the bulb EL1 lights up; at the same time, the normally open contact K-2 is reset and disconnected , cut off the power supply of the bulb EL2, and the bulb EL2 goes out.
The above is the introduction of the concept, circuit symbol, main function, basic structure and working principle of the relay. After more than one hundred years of development, relays have formed various forms, such as time relays, temperature relays, reed relays, thermal relays, differential relays, photorelays, sound relays, Hall relays, etc., and now there are solid state relays. Relays are available in various forms from mechanical to electronic.