A relay is an electrical control device. It has an interaction between the control system (also known as the input loop) and the controlled system (also known as the output loop).
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Often used in automated control circuits, it is actually an "automatic switch" that uses small currents to control large current operation. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.
When the input amount (such as voltage, current, temperature, etc.) reaches the specified value, the relay is turned on or off by the controlled output circuit.
The input quantity can be divided into two categories: electrical quantity (such as current, voltage, frequency, power, etc.) and non-electrical quantity (such as temperature, pressure, speed, etc.).
The relay has the advantages of fast action, stable operation, long service life and small volume. Widely used in power protection, automation, motion, remote control, measurement and communication devices.
Working principle and characteristics: Electromagnetic relays are generally composed of iron core, coil, armature, contact spring and so on. As long as a certain voltage is applied to both ends of the coil, a certain current flows in the coil, thereby generating an electromagnetic effect, and the armature will absorb the pulling force of the return spring against the iron core under the action of the electromagnetic force attraction, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position in the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are released. In this way, the suction and release are achieved, thereby achieving the purpose of turning on and off in the circuit. For the "normally open, normally closed" contacts of the relay, it can be distinguished as follows: a static contact that is in an open state when the relay coil is not energized, called a "normally open contact"; a static contact that is in an on state It is a "normally closed contact". Relays generally have two circuits, which are low voltage control circuits and high voltage working circuits.
The solid state relay is a kind of four-terminal device with two terminals as the input terminals and the other two terminals as the output terminals. The isolation device is used to realize the electrical isolation of the input and output.
Solid state relays can be classified into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, and the photoelectric isolation type is the most.
The thermal reed relay is a new type of thermal switch that uses temperature sensitive magnetic materials to detect and control temperature. It consists of a temperature-sensitive magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting piece, a plastic substrate, and Other Accessories. The thermal reed relay does not use coil excitation, and the magnetic force generated by the constant magnetic ring drives the switching action. Whether the constant magnetic ring can supply the magnetic force to the reed switch is determined by the temperature control characteristics of the temperature sensitive magnetic ring.
The reed relay is a relay that activates the reed switch by generating a magnetic field from the coil, and is a coil sensing device. Therefore, the characteristics of the reed relay, small size, light weight, fast response speed, short runout time and other characteristics.
When a piece of ferromagnetic metal or other magnetically permeable material is in close proximity, an action occurs, opening or closing the circuit. It consists of a permanent magnet and a reed switch. The permanent magnet and the reed switch are attached to a bracket that is non-magnetic and magnetic. Taking the line connecting the north and south poles of the permanent magnet as the axis, this axis should coincide with or substantially coincide with the axis of the reed switch. Adjusting the distance between the permanent magnet and the reed switch from far and near, when the reed switch just happens to move (for the normally open reed switch, it becomes closed; for the normally closed reed switch, it becomes disconnected) When fixing the position of the magnet. At this time, when there is a whole piece of magnetic conductive material, for example, the iron plate is close to the magnet and the reed switch at the same time, the reed switch will act again to return to the state when there is no magnetic field; when the iron plate leaves, the reed switch That is, the action in the opposite direction occurs. The reed relay has a solid structure, the contact is sealed, and has high durability. It can be used as a mechanical device "target=_blank> position limit switch for mechanical equipment. It can also be used to detect whether iron doors, windows, etc. are in the specified position.
The photo relay is a semiconductor relay used for AC/DC, and refers to a device in which a light-emitting device and a light-receiving device are integrated. The input side and the output side are electrically isolated, but the signal can be transmitted by optical signals.
Its characteristics are semi-permanent life, small current drive signal, high-impedance insulation withstand voltage, ultra-small, optical transmission, no contact, etc.
Mainly used in measuring equipment, communication equipment, security equipment, medical equipment, etc.
The time relay is a control device that realizes delay control by using electromagnetic principle or mechanical principle. It has many types, including air damping type, electric type and electronic type.
Air-damped time relays are often used in AC circuits, which use the principle of air throttling through small holes to obtain delayed action. It consists of three parts: the electromagnetic system, the delay mechanism and the contacts.
The time relay can be divided into two types: power-on delay type and power-off delay type.
The air damping type time relay has a large delay range (0.4 to 60 s and 0.4 to 180 s), and has a simple structure but low accuracy.
When the coil is energized (voltage specifications are ac380v, ac220v or dc220v, dc24v, etc.), the armature and the pallet are attracted by the core and instantaneously moved down, so that the instantaneous action contact is turned on or off. However, the piston rod and the lever cannot fall together with the armature because the upper end of the piston rod is connected to the rubber film in the air chamber. When the piston rod starts to move downward under the action of the release spring, the rubber film is then concave downward. The air in the air chamber becomes thin and the piston rod is dampened and slowly descends. After a certain period of time, the piston rod is lowered to a certain position, and the delay contact is actuated by the lever, so that the breaking contact is opened and the moving contact is closed. From the energization of the coil to the completion of the delay contact, this time is the delay time of the relay. The length of the delay time can be changed by adjusting the size of the air inlet of the air chamber with a screw.
After the attracting coil is de-energized, the relay is restored by the action of the return spring. Air is quickly expelled through the vent.
The relay is an automatic switching element with isolation function. It is widely used in remote control, telemetry, communication, automatic control, electromechanical "target=_blank> mechatronics and power electronics, and is one of the most important control components.
Relays generally have an inductive mechanism (input section) that reflects certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); it has the ability to "pass" and "control" the controlled circuit. The actuator (output portion) of the control unit is disconnected; between the input portion and the output portion of the relay, there is also an intermediate mechanism (drive portion) that couples the input amount, functions, and drives the output portion.
As a control element, in summary, the relay has the following effects:
1) Expand the control range: For example, when the multi-contact relay control signal reaches a certain value, it can switch, disconnect, and turn on multiple circuits at the same time according to different forms of the contact group.
2) Amplification: For example, sensitive relays, intermediate relays, etc., with a very small amount of control, can control a very high power circuit.
3) Integrated signal: For example, when a plurality of control signals are input to a multi-winding relay in a prescribed form, the comparison is integrated to achieve a predetermined control effect.
4) Automatic, remote control, monitoring: For example, the relay on the automatic device together with other electrical appliances can form a program control circuit to achieve automatic operation.
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