Because the relay is composed of two parts: a coil and a contact group, the graphical symbols of the relay in the circuit diagram also include two parts: a long box represents the coil; a group of contact symbols represents the contact combination. When the circuit is relatively simple with few contacts, the contact group is often drawn directly on one side of the coil frame. This drawing method is called centralized representation.
Electric symbol and contact form:
The relay coil is represented by a rectangular box symbol in the circuit. If the relay has two coils, draw two parallel rectangular boxes. At the same time, mark the text symbol "J" of the relay in or beside the long box. There are two ways to represent the contacts of the relay: one is to draw them directly on the side of the long box, which is more intuitive. The other is to draw each contact into its own control circuit 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 three basic forms of relay contacts:
1. The two contacts of the moving-on (normally open) (H type) coil are disconnected when the coil is not energized, and the two contacts are closed after energization. It is represented by the pinyin prefix "H" of the ligature.
2. When the dynamic-break (normally closed) (D type) coil is not energized, the two contacts are closed, and the two contacts are disconnected after energization. It is indicated by the pinyin prefix "D" of hyphenation.
3. Conversion type (Z type) This is a contact group type. This kind of contact group has three contacts in total, that is, the middle is a moving contact, and the upper and lower are static contacts. When the coil is not energized, the movable contact and one of the static contacts are disconnected and the other is closed. After the coil is energized, the movable contact moves to make the original open into closed, and the original closed into open state, and the conversion is achieved. purpose. Such contact groups are called changeover contacts. It is indicated by the pinyin prefix "z" of the word "zhuan".
Folding working principle and characteristics
Power direction relay
When the input (such as voltage, current, temperature, etc.) reaches the specified value, the electrical appliance that makes the controlled output circuit turn on or off. It can be divided into two categories: electrical relays (such as current, voltage, frequency, power, etc.) and non-electric relays (such as temperature, pressure, speed, etc.). It has the advantages of fast action, stable work, long service life and small size. It is widely used in power protection, automation, sports, remote control, measurement and communication devices. 
Electromagnetic relay is generally composed of iron core, coil, armature, contact reed, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, which will produce electromagnetic effects. Under the action of electromagnetic force, the armature will overcome the pull force of the return spring and attract to the core, thereby driving the armature. The moving contact and the static contact (normally open contact) are pulled together. When the coil is de-energized, the electromagnetic attraction will disappear, and the armature will return to its original position under the reaction force of the spring, releasing the moving contact and the original static contact (normally closed contact). This pulls in and releases, so as to achieve the purpose of conducting and cutting off in the circuit. The "normally open and normally closed" contacts of the relay can be distinguished as follows: the static contact that is in the off state when the relay coil is not energized is called "normally open contact"; the static contact that is in the on state is called It is "normally closed contact". Relays generally have two circuits, a low-voltage control circuit and a high-voltage working circuit.
Solid State Relay (SSR)
A solid state relay is a four-terminal device with two terminals as input and the other two terminals as output. An isolation device is used in the middle to achieve electrical isolation between input and output.
Solid state relays can be divided 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, with the photoelectric isolation type being the most.
The solid-state relay dedicated to solid-state relays can have short-circuit protection, overload protection and overheating protection functions, and the combination logic solidification package can realize the intelligent module required by the user and directly use it in the control system. Solid state relays have been widely used in computer peripheral interface equipment, constant temperature systems, temperature adjustment, electric furnace heating control, motor control, CNC machinery, remote control systems, industrial automation devices; signal lights, dimming, flashers, lighting stage lighting control systems; Instruments and meters, medical equipment, photocopiers, automatic washing machines; automatic fire protection, security systems, and the switch of power capacitors used as power factor compensation for power grids, etc. In addition, there are a large number of explosion-proof, moisture-proof, and anti-corrosion occasions in the chemical industry and coal mines. use.
Thermal Reed Relay
The thermal reed relay is a new type of thermal switch that uses thermal magnetic materials to detect and control temperature. It is composed of a temperature-sensitive magnetic ring, a constant magnetic ring, a dry reed tube, a thermally conductive mounting sheet, a plastic substrate and some other accessories. The thermal reed relay does not use coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch. Whether the constant magnetic ring can provide magnetic force to the reed tube is determined by the temperature control characteristics of the temperature-sensitive magnetic ring.
A reed relay is a relay in which a coil generates a magnetic field to actuate the reed tube, and is a coil sensing device. Therefore, the characteristics of the reed relay, small size, light weight, fast response speed, short bounce time and other characteristics.
When a whole piece of ferromagnetic metal or other magnetically conductive material approaches it, an action occurs to open or close the circuit. It is composed of permanent magnet and reed pipe. The permanent magnet and the reed switch are fixed on a bracket that is neither magnetic nor magnetic. Taking the line connecting the north and south poles of the permanent magnet as the axis, this axis should coincide or substantially coincide with the axis of the reed switch. Adjust the distance between the permanent magnet and the reed pipe from far to near, when the reed pipe just happens to move (for a normally open reed pipe, it becomes closed; for a normally closed reed pipe, it becomes open) When, fix the position of the magnet. At this time, when a whole piece of magnetically conductive material, such as an iron plate, is close to the magnet and the reed pipe at the same time, the reed pipe will act again and return to the state when there is no magnetic field; when the iron plate leaves, the reed pipe That is, an action in the opposite direction occurs. The reed relay has a sturdy structure, sealed contacts and high durability. It can be used as a position limit switch for mechanical equipment, and it can also be used to detect whether iron doors, windows, etc. are in designated positions.
The photorelay is a semiconductor relay that uses AC/DC and refers to a device that integrates a light-emitting device and a light-receiving device. The input side and output side are electrically insulated, but the signal can be transmitted by optical signal.
Its characteristics are semi-permanent life, small current drive signal, high impedance insulation withstand voltage, ultra-small size, optical transmission, no contact... etc.
Mainly used in measurement equipment, communication equipment, security equipment, medical equipment... etc.
Time relay is a kind of control electric appliance that uses electromagnetic principle or mechanical principle to realize delay control. It has many types, including air damping type, electric type and electronic type.
Air damping time relays are often used in AC circuits, which use the principle of throttling air through small holes to obtain delay action. It is composed of three parts: electromagnetic system, delay mechanism and contacts.
Time relays can be divided into two types: power-on delay type and power-off delay type.
The air damping time relay has a large time delay range (with 0.4～60s and 0.4～180s). It has a simple structure but low accuracy.
When the coil is energized (voltage specifications are ac380v, ac220v or dc220v, dc24v, etc.), the armature and pallet are attracted by the iron core and move down instantaneously, making the instantaneous action contact on or off. However, the piston rod and lever cannot fall with the armature at the same time, 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 concave downward. The air in the air chamber becomes thin and the piston rod is damped and slowly descends. After a certain period of time, the piston rod descends to a certain position, and the delay contact action is pushed through the lever to make the moving break contact open and the moving make contact close. The time from when the coil is energized to when the delay contact completes the action is the delay time of the relay. The length of the delay time can be changed by adjusting the size of the air inlet hole of the air chamber with a screw.
After the suction coil is de-energized, the relay relies on the recovery spring to recover. The air is quickly exhausted through the air outlet.
Features of intermediate relay:
The relay is composed of multiple high-quality sealed small relays with lower coil voltage, moisture-proof, dust-proof, uninterrupted wire, and high reliability. It overcomes the shortcomings of electromagnetic intermediate relay wires that are too thin and easy to break; low power consumption and low temperature rise , No need to attach a high-power resistor, it can be installed and connected at will; the relay has large contact capacity and long working life; after the relay is activated, there is a light-emitting tube indicator, which is convenient for on-site observation; the delay only needs to be set by the dial switch on the panel , The delay accuracy is high, and the delay range can be arbitrarily set between 0.02-5.00S.
The purpose of the intermediate relay:
Intermediate relays are used in various protection and automatic control circuits to increase the number of contacts and contact capacity of the protection and control circuits.
Classification of intermediate relays:
Low current start intermediate relay
Static intermediate relay
Delay intermediate relay
Electromagnetic intermediate relay
Intermediate relay for elevator
Rail type intermediate relay