Relay is a common electrical control component, which is a device that utilizes electromagnetic principles to control the switching of a circuit. In life, relays are widely used in a variety of automated control circuits, such as home appliances, industrial equipment, transportation and so on. So, what is the working principle of the relay? And what applications does it have? This article will take you to understand the principle and application of relays.

What is a relay?

Relays are automatic control devices that use electromagnetic principles to turn on and off circuits. They are commonly used in automation control, signal switching, and circuit protection scenarios. When the input signal (such as current, voltage, etc.) reaches a predetermined value, the contacts are driven to close or disconnect via the internal electromagnetic system, allowing for the control of other circuits.

Components of Relay

①Electromagnetic system

Electromagnetic system is the core part of the relay, which mainly includes iron core, coil and yoke. When the coil is energized, a magnetic field is generated, the size of which is proportional to the square of the current. The role of the iron core and yoke is to strengthen the magnetic field and improve the action sensitivity of the relay.

②Contact System

The relay's actuation component, the contact system, is primarily made up of both static and dynamic contacts. When the electromagnetic system's magnetic field reaches a certain level, the force of the magnetic field will overcome the release spring's elasticity, closing the movable and static contacts and achieving a circuit connection; when the coil is de-energized, the magnetic field vanishes, and the release spring's elasticity causes the movable and static contacts to disconnect, achieving a circuit cut-off.

"Normally open contacts" are static contacts that are in the open state; "normally closed contacts" are static contacts that are in the on state. The relay coil is not activated when these contacts are in the open state.

③Release spring

Release spring is an important part of the relay, its role is to make the contact system in the absence of electromagnetic force to maintain the disconnected state. When the coil is energized, the magnetic force overcomes the spring force of the release spring and closes the contact system; when the coil is de-energized, the magnetic field disappears and the spring force of the release spring breaks the contact system.

Principle of operation of a relay

The working principle of a relay is mainly based on electromagnetic induction. When the relay coil is energized, it generates an electromagnetic field that attracts the iron core, which closes the iron core and the contacts, thus realizing the on-off of the control circuit. Specifically, the relay is mainly composed of the following parts:

1. Coil: when the current passes through the coil, a magnetic field is generated, and the size of the magnetic field is proportional to the current strength.

2. Iron core: the role of the iron core is to enhance the magnetic force of the coil magnetic field, so that the contacts closed.

3. Contacts: The contacts are the switching part of the relay and are categorized into normally closed and normally open contacts. When the iron core is attracted, normally closed contacts are disconnected, normally open contacts are closed; when the iron core is released, normally closed contacts are closed, normally open contacts are disconnected.

4. Shell: shell used to protect the internal components to prevent the entry of dust, moisture and so on.

Relay applications

Relay in life and industry has a wide range of applications, the following are a few common examples of applications:

1. Household appliances: in household appliances, relays are often used to control the power supply on and off, such as air conditioners, refrigerators, washing machines and so on. In addition, the relay can also be used to adjust the voltage and current, such as dimming lights, speed fans, etc. 2.

2. Industrial equipment: In industrial production, relays can be used in automated control circuits, such as robot motion control, material transportation on production lines. Relays can also be used for protection circuits, such as overload protection, short-circuit protection, etc.

3. Transportation: In automobiles, trains, airplanes and other means of transportation, relays are used to control the switching of various electrical equipment, such as on-board air conditioning, lighting, audio and so on. In addition, relays are also used to control key components such as engines and braking systems.

4. Computers: In computers, relays are used to control external devices such as power supplies, printers, scanners, and so on. In addition, relays are used to control the cooling system of computers, such as cooling fans.

Relay is a kind of electrical control equipment, which is mainly based on the change of the input quantity (current, voltage, resistance, etc.), and then through electromagnetic effect or electro-thermal effect, etc. to produce physical quantities (e.g., displacement, pressure, heat, etc.), so as to make the controlled system to achieve the predetermined goal of a kind of automatic switch. Relay in the electrical control system plays a vital role, it can realize the automatic control of the circuit, protection and regulation and other functions.

Relay is mainly composed of electromagnetic system, contact system and release spring. When the input of the relay changes, the magnetic field generated by the electromagnetic system will also change, thus driving the closure and disconnection of the contact system to realize the control of the circuit. Relays generally have two circuits, one for control and the other for operation.

Types of Relays

The following are the main types of relays in common use:

Voltage relays: Voltage relays are relays that realize circuit control according to the change of input voltage. Voltage relays have many turns of coil, thin wires, and high impedance, and are commonly used in power system relay protection to reflect the change of voltage in the circuit and for voltage protection of the circuit. Voltage relays can be divided into undervoltage relays and overvoltage relays.

Intermediate relay: one of the most commonly used relays, its structure is basically the same as the contactor. It is characterized by small size and high sensitivity of action. The function of intermediate relay is to control large current with small current. In the load capacity is relatively small, the intermediate relay can replace the small contactor. Intermediate relays can be used to extend the capacity and number of contacts and to transmit intermediate signals in the control circuit. An intermediate relay is essentially a voltage relay.

Figure. 1

Current Relay: A current relay is a relay that controls a circuit based on a change in input current. The coil of a current relay is strung into the circuit to reflect the change in circuit current, and has fewer turns, thicker wires, and lower impedance.

Time relay: an automatic control appliance that utilizes electromagnetic principles or mechanical action principles to delay contact closure or breakage. In many control systems, time relays can be used to achieve time-delay control, in the circuit to play a delayed closure or disconnection.

Thermal relay: When the heat generated by the input current reaches the set value, the thermal relay will automatically act to realize the cut-off of the circuit to protect the circuit from damage. Thermal relays are mainly used for overload protection of three-phase motors, phase break protection or three-phase current imbalance and other electrical equipment heat state control. Note: Thermal relays cannot be used for instantaneous overload protection or short circuit protection.

Pressure relays: Pressure relays are relays that realize circuit control according to the pressure of input gas or liquid.

The main use of the relay

①Automatic control

Relay can be based on changes in the input quantity, through the electromagnetic effect or electro-thermal effect and other physical quantities, and other electrical appliances together to form a program control route to achieve automatic control. For example, automatic control of motor start, stop and forward and reverse.

②Circuit protection

Through the relay according to the different forms of contact combinations, you can simultaneously switch, open and close multiple circuits, to achieve the protection of the circuit. Such as overload protection, short circuit protection and leakage protection.

③Signal conversion

Relay can realize the conversion of signals, such as electrical signals into mechanical signals or pneumatic signals.

④ Function Expansion

The relay can realize the expansion of the circuit function to realize the multi-channel control, sequence control and time-delay control.