What is a relay? What are its advantages?

What is a relay? What are its advantages?
Post Date:2024-10-25,

What is a Relay?

Relay is a kind of electrical control device, which is an electrical appliance that makes a predetermined step change in the controlled quantity in the electrical output circuit when the change of the input quantity (excitation quantity) reaches 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 the control circuit of automation, it is actually a kind of "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.


Relays generally have an induction mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); There is an actuator (output part) that can realize "on" and "off" control of the controlled circuit; Between the input and output parts of the relay, there is also an intermediate mechanism (drive part) that couples and isolates the input quantity, processes the function, and drives the output part.
What is a relay? What are its advantages?

How do relays work?

Relays work on the principle of electromagnetic effects, and their core components include coils, cores, armatures, and contact reeds, among others. When a certain voltage is added to both ends of the coil, an electric current flows through the coil, resulting in an electromagnetic effect, and the armature overcomes the tensile force of the spring under the action of electromagnetic force to attract the core, driving the dynamic contact to engage with the static contact. When the coil is de-energized, the electromagnetic attraction disappears, the armature returns to its original position under the reaction force of the spring, and the moving and static contacts are engaged again. This process of engagement and release realizes the circuitTurn-on and cut-off.
What is a relay? What are its advantages?

What is the purpose of a relay?

As a control element, in summary, the relay has the following functions:

(1) Expand the control range: for example, when the control signal of the multi-contact relay reaches a certain value, it can be changed, interrupted and connected to multiple circuits at the same time according to the different forms of the contact group.


(2) Amplification: For example, sensitive relays, intermediate relays, etc., can control very high-power circuits with a very small control amount.


(3) Comprehensive signal: For example, when a plurality of control signals are input into a multi-winding relay in the specified form, the predetermined control effect is achieved after comparative synthesis.


(4) Automatic, remote control, monitoring: For example, the relay on the automatic device and other electrical appliances can form a program control circuit, so as to achieve automatic operation.

What are the classifications of relays?

There are many types of relays:
1. According to the input amount, it can be divided into voltage relay, current relay, time relay, speed relay, pressure relay, etc.;
2. According to the working principle, it can be divided into electromagnetic relays, inductive relays, electric relays, electronic relays, etc.;
3. According to the application, it can be divided into control relays, protection relays, etc., and can be divided into relays with or without relays and measurement relays according to the form of input changes.
The relay does not operate when there is no input, and the relay acts when there is an input amount, such as intermediate relays, general relays, time relays, etc.
The measurement relay is based on the change of the input quantity to act, the input amount is always there when working, only when the input amount reaches a certain value when the relay acts, such as current relay, voltage relay, thermal relay, speed relay, pressure relay, liquid level relay, etc.

Contacts for relays

The relay coil is represented by a rectangular box symbol in the circuit, and if the relay has two coils, draw two rectangular boxes side by side. At the same time, mark the word symbol "J" of the relay in or next to the rectangular box.


There are two ways to represent the contacts of a relay: one is to draw them directly on the side of the rectangular box, which is more intuitive. The other is to draw each contact into their respective control circuits according to the needs of circuit connection, usually the same text symbol is marked next to the contact and coil of the same relay, and the contact group is numbered to show the difference.


There are 3 basic forms of relay contacts:

(1) The two contacts are disconnected when the dynamic type (normally open, H-type) coil is not energized, and the two contacts are closed after the energizing is applied. It is represented by the pinyin prefix "H".


(2) The two contacts are closed when the coil is not energized, and the two contacts are disconnected after the energizing is on. It is represented by the pinyin prefix "D" of the word "broken".


(3) The conversion type (Z type) is a contact set type. This type of contact group has a total of 3 contacts, i.e. a moving contact in the middle and a static contact at the top and bottom. When the coil is not energized, the moving contact and one of the static contacts are disconnected and the other is closed; When the coil is energized,The moving contact will move, so that the original disconnected is closed, and the original closed is disconnected, so as to achieve the purpose of conversion. Such a set of contacts is called a conversion contact. It is represented by the pinyin prefix "Z" of the word "turn".
What is a relay? What are its advantages?

What are the advantages of relays?

1. Low cost: The manufacturing cost of the relay is relatively low, the service life is long, and the maintenance is convenient.


2. Separation control: The relay realizes electrical isolation, which can avoid the influence of electrical equipment on the controller, and at the same time can convert the low-voltage signal into a high-voltage signal.


3. Good safety: the relay can realize a variety of protection measures such as leakage protection, overload protection, overvoltage protection, etc., so as to ensure the safe and stable operation of the equipment.


4. Reliable contacts: The contacts of the relay adopt a mechanical structure, which has good mechanical strength and stability, which ensures the reliability of the contacts.


5. Strong load capacity: The relay can control high-power loads, such as high voltage, high current, etc., to adapt to various electrical control needs.


6. Multiple types: There are many different types of relays, such as electromagnetic relays, solid-state relays, etc., which can meet different application needs.


7. Flexible adaptation: The relay is suitable for various electrical control systems, and can flexibly control the switching of circuits, with strong adaptability.


8. Safe and reliable: The relay can be isolated and protected to avoid circuit failure caused by load failure, etc., and improve safety.

What are the disadvantages of relays?

1. Vulnerable to damage: The contacts in the relay are susceptible to arc and welding, resulting in poor contact, loose wiring and other problems, which affect the stability and reliability of the circuit.


2. High noise: The relay will produce noise when switching, especially when used at high frequencies.


3. Easy to misoperate: There is a problem of misoperation of relays, that is, the magnetic field of the wires present at the same current interferes with the operating current of the relay, resulting in the misoperation of the relay. This not only affects the normal operation of the equipment, but also reduces the stability of the circuit.

Wiring method of relay:

1. Normally open connection method
Normally open connection means that when the relay is working, the contact of the relay is closed at first, and the contact of the relay will be disconnected when the control signal is triggered.

The normally open connection method is suitable for occasions where the circuit can only be turned on and off after the control signal is triggered, such as lighting circuits.

What is a relay? What are its advantages?

2. Normally closed connection method
The normally closed connection method means that when the relay is working, the contact of the relay is in an open state at first, and the contact of the relay will be closed when the control signal is triggered.

The normally closed connection method is suitable for occasions where the circuit can only be turned on and off when the control signal disappears, such as motor control.


3. Intermediate contact connection
The intermediate contact connection method means that the relay has two contacts, one is normally open contact and the other is normally closed contact, when the control signal is triggered, the intermediate contact is turned on, and when the control signal disappears, the intermediate contact is disconnected.
The intermediate contact connection method is suitable for situations where it is necessary to switch between the two states of the control signal, such as security access control.
For different applications, it is better to choose different relay wiring methods to meet a variety of needs.

What are the application areas of relays?

Relays are widely used in many fields, including power systems, automation control, communication equipment, transportation, and household appliances

1. Power system: Relays play an important role in the power system, mainly used for protection, control, measurement, etc. For example, they are used for the protection and control of generators, transformers, electric motors, etc.


2. Automatic control: The relay is a key component in the automatic control system, which is used to realize various automatic control functions. They control large currents with small currents to achieve functions such as automatic regulation, safety protection, and circuit conversion.


3. Communication equipment: In the field of communication, relays are used to realize functions such as signal switching and power control to ensure the normal operation of communication equipment.


4. Transportation: Relays are also widely used in the field of transportation, including railways, highways, aviation and ships. They are used for signal light control, motor drive, and other functions to ensure the safety and smoothness of transportation.


5. Household appliances: relays are widely used in household appliances, such as televisions, washing machines, refrigerators, etc. Relays are able to convert small electrical signals into large currents to control the switching of electrical appliances. For example, when we press the switch button on the TV, the relay inside the TV turns on, which energizes the power line of the TV and turns it on.


6. Aerospace: Due to the harsh environment in the aerospace field, relays are also widely used in this field. Relays can control the switches of aircraft, satellites and other equipment to ensure their normal operation.


In addition, relays are also used in ships and other fields to complete the functions of signal transmission, execution control, system power distribution, etc.and are one of the key electronic components in each system

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