What Are the Different Types of Electromagnetic Device?

Electromagnetic compatibility (EMC) refers to the ability of a device or system to operate in accordance with requirements in its electromagnetic environment without causing unbearable electromagnetic interference to any device in its environment. Therefore, EMC includes two requirements: on the one hand, it means that the electromagnetic interference generated by the equipment in the environment during normal operation cannot exceed a certain limit; on the other hand, it means that the equipment has certain electromagnetic interference in the environment. Degree of immunity, ie electromagnetic sensitivity.

EMC (ElectromagneticCompatibility)

In the International Electrotechnical Commission standard IEC, the definition of electromagnetic compatibility is: the system or equipment can work normally in the electromagnetic environment in which it is located, and it will not cause interference to other systems and equipment.

EMC includes EMI (Electromagnetic Interference) and EMS (Electromagnetic Tolerance). The so-called EMI electromagnetic interference is the electromagnetic noise generated by the machine itself in the process of performing due functions, which is detrimental to other systems. The ability to be protected from the surrounding electromagnetic environment in performing its intended function.

Electromagnetic compatibility (electromagneticcompatibility) The ability of various electrical or electronic equipment to meet the design's normal working requirements in a common space with a complex electromagnetic environment with a specified safety factor. Also called electromagnetic compatibility. Its meaning includes:

mutual consideration between electronic systems or equipment in the electromagnetic environment;

The electronic system or equipment can work normally in accordance with the design requirements in the electromagnetic environment of nature. If it is further extended to the impact of electromagnetic fields on the ecological environment, the subject of electromagnetic compatibility can be called environmental electromagnetics.

Various operating power equipment are related to each other and affect each other in three ways: electromagnetic conduction, electromagnetic induction, and electromagnetic radiation. Under certain conditions, it will cause interference, impact and harm to the operating equipment and personnel.

The EMC discipline that emerged in the 1980s is aimed at studying and solving this problem. It is mainly to study and solve the generation, propagation, reception, and suppression mechanisms of interference and their corresponding measurement and metrology technologies. Based on this, The most reasonable principle of technology and economy, make clear regulations on the interference level, anti-interference level and suppression measures, so that the equipment in the same electromagnetic environment are compatible, and it is not allowed to introduce to any entity in the environment. Electromagnetic disturbance.

Institutions that conduct electromagnetic compatibility (including electromagnetic interference and electromagnetic tolerance) detection and testing include laboratories such as the Suzhou Electrical Research Institute, the Aerospace Environmental Reliability Test Center, and the Environmental Reliability and Electromagnetic Compatibility Test Center.

Internal interference refers to the mutual interference between various components inside an electronic device, including the following:

(1) Interference caused by leakage caused by the working power supply through the distributed capacitance and insulation resistance of the line; (related to the operating frequency)

(2) The signals are coupled to each other through the impedance of the ground wire, power supply and transmission wires, or interference caused by mutual inductance between the wires;

(3) Some components inside the equipment or system generate heat, affecting the interference caused by the component itself or the stability of other components;

(4) The magnetic and electric fields generated by high-power and high-voltage components affect the interference caused by other components through coupling.

External interference refers to the interference of lines, equipment or systems by factors other than electronic equipment or systems, including the following:

(1) External high voltage and power supply interfere with electronic circuits, equipment or systems through insulation leakage;

(2) External high-power equipment generates a strong magnetic field in the space and interferes with electronic circuits, equipment or systems through mutual inductance coupling;

(3) the interference of space electromagnetic waves on electronic circuits or systems;

(4) The unstable working environment temperature causes interference caused by changes in the parameters of electronic circuits, equipment or internal components of the system;

(5) Interference caused by equipment powered by the industrial grid and by grid voltage through power transformers.

Rapid development of electromagnetic compatibility technology

There are electromagnetic waves everywhere in the space of thousands of kilometers from the earth's surface to the activities of artificial satellites. Electricity and magnetism affect people's lives and productions all the time. The widespread application of electromagnetic energy makes the development of industrial technology change rapidly. While electromagnetic energy creates huge wealth for human beings, it also brings certain harm. It is called electromagnetic pollution. The study of electromagnetic pollution is an important branch of environmental protection. In the past, people referred to the interference of radio communication devices as electromagnetic interference, which indicates that the device was harmed by external interference. In fact, it also caused harm to other external devices, and became a source of interference. Therefore, the interference and interference of the device must be studied at the same time. Attention must be paid to the compatibility between the internal organization of the device and the device. With the development of science and technology, the increasingly widely adopted microelectronic technology and the gradual realization of electrification have formed a complex electromagnetic environment. Continuously researching and solving the problem of the relationship between equipment and systems in the electromagnetic environment has promoted the rapid development of electromagnetic compatibility technology.

Requirements for electromagnetic compatibility design: Clear the system's electromagnetic compatibility indicators. The electromagnetic compatibility design includes the electromagnetic interference environment in which the system can maintain normal work and the allowable indicators of the system's interference with other systems. On the basis of understanding the interference source, the victim, and the interference path of the system, these indicators are assigned to each sub-system, subsystem, circuit, component, and device step by step through theoretical analysis. According to the actual situation, take corresponding measures to suppress interference sources, eliminate interference channels, and improve the anti-interference ability of the circuit. Through experiments to verify whether the original target requirements have been met, if not, then take further measures and cycle several times until the original target is reached.

Divided into natural and artificial. Natural interference sources mainly include various phenomena that occur in the atmosphere, such as noise caused by lightning, snow, rain, hail, and sandstorms. Natural interference sources also include cosmic noise from the sun and outer space, such as solar noise, interstellar noise, and galactic noise. There are various sources of artificial interference, such as various signal transmitters, oscillators, motors, switches, relays, neon lights, fluorescent lights, engine ignition systems, electric bells, heaters, arc welding machines, high-speed logic circuits, gate circuits, Thyristor inverter, gas rectifier, corona discharge, various industrial, scientific and medical high-frequency equipment, urban noise, noise caused by electric railways, and nuclear electromagnetic pulses generated by nuclear explosions.

Can be divided into two types: conducted interference and radiated interference. Interference propagating along a conductor is called conducted interference, and its propagation modes are electrical coupling, magnetic coupling, and electromagnetic coupling. Electromagnetic interference that is transmitted in the form of electromagnetic waves through space is called radiated interference, and its propagation methods include near-field induction coupling and far-field radiation coupling. In addition, conducted interference and radiated interference may also coexist, thereby forming a composite interference.

Various artificial noises, such as power line corona noise, car noise, contactor noise, and noise caused by discharge when the conductor is opened, electric locomotive noise, urban noise, etc.

The influence of various public utilities equipment (power transmission line, communication, railway, highway, petroleum metal pipeline, etc.) in the shared corridor.

Reflection problems caused by large buildings such as super high-rise buildings, transmission lines, and iron towers.

Effects of electromagnetic environment on humans and various living things. These include the power frequency fields such as strong wires, the effects of medium, short wave and microwave electromagnetic radiation.

Influence of nuclear electromagnetic pulse. The electromagnetic pulses generated by high-altitude nuclear explosions can destroy command, control, communication, computer, and reporting systems on the ground in a large area.

TEMPEST technology. Its essential content is a series of research work on information reception and protection from the aspects of electromagnetic radiation and information leakage of information equipment.

Malfunction of electronic equipment. In order to prevent malfunction, measures must be taken to improve the anti-interference ability of the equipment.

Spectrum allocation and management. Radio frequency spectrum is a limited resource, but it is not consumable. It must be scientifically managed and fully utilized.

Electromagnetic compatibility and measurement.

Nature influence, etc.

Use a complete shield to prevent external radiation from entering the system and prevent interference energy from radiating out of the system. The shield should be kept intact, the necessary doors, seams, ventilation holes and cable holes must be properly handled, and the shield must be reliably grounded.

Design a reasonable grounding system. Separate the ground for small signals, large signals, and interference circuits as much as possible, and ground resistance should be as small as possible.

Use appropriate filtering technology. The passband of the filter is selected reasonably to minimize leakage loss.

Using limiting technology, the limiting level should be higher than the working level, and it should be limited in both directions.

Select the connection cable and wiring method correctly. If necessary, use optical cables instead of long cables.

Adopt technologies such as balanced differential circuit, shaping circuit, integrating circuit and gating circuit.

System frequency allocation should be appropriate. When there are multiple main frequency signals working in a system, try to avoid the frequency of each signal, or even the resonance frequency of the other side.

When the conditions permit, the various equipment in the shared corridor should maintain a large distance to reduce their mutual influence.

Due to the increasing dependence of microcomputers and the large use of equipment, our electromagnetic environment is complicated. Therefore, external interference such as impulse noise, radiated electromagnetic fields, static electricity, lightning strikes, voltage changes, etc., may cause malfunctions or even damage caused by malfunctions. Situations such as radio communications, radars, big brothers, and television game instruments often interfere with televisions and even cause malfunctions in the use of medical equipment, affecting the safety of flight.

Internationally, more and more attention has been paid to the immunity test of electronics, electrical appliances, and industrial equipment products, and it has tended to integrate the IEC (International Electrotechnical Commission) international test standard as the test standard. The European Community took the lead in formulating EMC prevention regulations and began to implement immunity tests in 1996.

The so-called electromagnetic interference refers to any electromagnetic phenomenon that can degrade equipment or system performance. The so-called electromagnetic sensitivity refers to the degradation of the equipment or system due to electromagnetic interference.

Electromagnetic interference (Electromagnetic Interference), referred to as EMI, has two types: conducted interference and radiated interference. Conducted interference mainly refers to the interference signals generated by electronic devices that interfere with each other through conductive media or public power lines; radiated interference refers to the interference signals generated by electronic devices that pass the interference signals to another electrical network or electronic device through spatial coupling.

In order to prevent electromagnetic interference generated by some electronic products from affecting or disrupting the normal operation of other electronic equipment, governments or international organizations of various countries have successively proposed or formulated some relevant regulations or standards for electromagnetic interference to electronic products. Products that meet these regulations or standards It can be called EMC (Electromagnetic Compatibility). The EMC standard is not constant, but it is changing every day. This is also the method often adopted by governments or economic organizations to protect their own interests.

The first measure to suppress electromagnetic pollution is to find the source of the pollution; the second is to judge the path of pollution intrusion. There are mainly two ways of conduction and radiation. The focus of work is to determine the amount of interference. Solving electromagnetic compatibility problems should start from the product development stage and run through the entire product or system development and production process. A lot of experience at home and abroad shows that the earlier you pay attention to solving electromagnetic compatibility problems during the development and production of products or systems, the more you can save manpower and material resources.

The key technology of electromagnetic compatibility design is to study the source of electromagnetic interference, and controlling its electromagnetic emission from the source of electromagnetic interference is the method to cure the root cause. To control the emission of interference sources, in addition to reducing the level of electromagnetic noise generated from the mechanism of electromagnetic interference sources, shielding (including isolation), filtering, and grounding techniques need to be widely applied.

The shield is mainly made of various conductive materials and manufactured into various shells and connected to the earth to cut off the electromagnetic noise propagation path formed by electrostatic coupling, inductive coupling or alternating electromagnetic field coupling in the space. The isolation mainly uses relays, isolation transformers or photoelectricity. Isolators and other devices cut off the propagation path of electromagnetic noise in a conductive form. Its characteristics are to separate the ground system of the two parts of the circuit and cut off the possibility of coupling through impedance.

Filtering is a technique for processing electromagnetic noise in the frequency domain. It provides a low-impedance path for electromagnetic noise to achieve the purpose of suppressing electromagnetic interference. For example, a power filter presents a high impedance to a power frequency of 50 Hz and a low impedance to the electromagnetic noise spectrum.

Grounding includes grounding, signal grounding, and so on. The design of the grounding body, the arrangement of the ground wire, and the impedance of the ground wire at various frequencies are not only related to the electrical safety of the product or system, but also related to electromagnetic compatibility and its measurement technology.

For the system to have electromagnetic compatibility problems, there must be three factors, namely the source of electromagnetic disturbance, the coupling path, and sensitive equipment. Therefore, when encountering electromagnetic compatibility problems, we must start with these three factors, apply the right medicine, and eliminate one of them to solve the electromagnetic compatibility problem.

(1) Equipment refers to any electrical, electronic or electromechanical device that works as an independent unit and performs a single function.

(2) System (system) refers to "a number of equipment, sub-systems, full-time personnel, and technical combinations that can perform or guarantee work tasks."

Electromagnetic compatibility (EMC) is divided into electromagnetic interference (EMI) and electromagnetic tolerance (EMS). All electronic products must comply with the general regulations of electromagnetic compatibility.

The problem of electromagnetic compatibility is under the continuous application of high-tech technology in various products such as electronics, motors, information, and communications. In addition to users' requirements for communication quality, they are also actively regulated by governments in various countries to regulate them. The importance and urgency of related issues. For example, Europe has strengthened post-market inspections of imported products, causing many checkpoints.

1. Electromagnetic compatibility 1. foreign standards

EN55014-1 electromagnetic interference

EN55014-2 electromagnetic immunity

EN60555-2 / EN61000-3-2 power harmonic detection

EN60555-3 / EN61000-3-3 voltage flicker detection

EN61000-4-2 (ESD) ESD immunity test

EN61000-4-3 ESD immunity test

EN61000-4-4 (EFT / B) electrical fast pulse group anti-interference detection

EN61000-4-5 (Surge) Lightning Strike Anti-Interference Detection

EN61000-4-6 (CS) conducted immunity test

EN61000-4-8 Power frequency magnetic field anti-interference detection

EN61000-4-11 (V.Dips) voltage transient drop anti-interference detection

EN61000-4-12 oscillating wave surge

EN61000-4-13 (Harmonic & interharmonics)

2. Electromagnetic compatibility 2. Domestic standards

CISPR15: 2005 Limits and measurement methods for radio disturbance characteristics of electrical lighting and similar equipment

GB / T19287 General requirements for immunity of telecommunication equipment

YD / T1536.1 Electromagnetic information security requirements and measurement methods for telecommunication equipment

YD / T1312 electromagnetic compatibility requirements and measurement methods for wireless communication equipment

GB1565 Urban Radio Noise Measurement Method

GB6833 Electromagnetic compatibility test specification for electronic measuring instruments

GB / T17626 electromagnetic compatibility test and measurement technology

GB / T12572-2008 General requirements and measurement methods for radio transmitting equipment parameters

GB / T26256-20102.4GHz band radio communication equipment mutual interference limitation and coexistence requirements and test methods

Technical specifications and measurement methods of GB / T21646-2008400MHz frequency band analog public radio

GB8702-1988 electromagnetic radiation protection regulations

GB917588 environmental electromagnetic health standard

GB1263890 Radiation safety requirements for microwave and ultrashort wave communication equipment