EMI & EMS & EMC

Emi--electro Magnetic interference Electromagnetic interference

definition: refers to the electromagnetic wave and electronic components after the action of the interference phenomenon.

Category: There are two kinds of conduction interference and radiation interference.

Conduction disturbance:

is the coupling (interference) of a signal from one electrical network to another by means of a conductive medium.

Radiated interference:

Refers to the interference source through space to its signal coupling (interference) to another electrical network.

Source: in high-speed PCB and system design, high-frequency signal line, IC pin, all kinds of connectors can become the antenna characteristics of the radiation interference source, can emit electromagnetic waves and affect other systems or other subsystems in the system normal work.

Electromagnetic Interference elements: The research of theory and practice shows that no matter the complex system or the simple device, the occurrence of any electromagnetic interference must have three basic conditions: first, there should be a source of interference, and secondly there is the way and channel to spread the disturbance energy; The third must also have the response of the disturbed object. In the electromagnetic compatibility theory, the system of the disturbed object is called the sensitive device (or the sensor).

Therefore, the electromagnetic disturbance source, the harassment transmission path (or the transmission channel) and the sensitive equipment are called the electromagnetic interference three elements.

1, electromagnetic harassment source classification

There are many methods of classifying electromagnetic disturbance sources.

1.1, generally speaking, the source of electromagnetic interference is divided into two categories: natural interference source and human disturbance source.

The source of natural disturbance originates mainly from the spherics noise of the atmosphere and the cosmic Noise of Earth outer space. They are not only the basic elements of the electromagnetic environment of the Earth, but also the source of interference to radio communication and space technology. Natural noises interfere with the operation of satellites and spacecraft, and also interfere with the launch of a ballistic missile launch vehicle.

The source of human disturbance is electromagnetic energy interference caused by electromechanical or other artificial device, which is a device specially used for transmitting electromagnetic energy, such as radio equipment such as radio, television, communication, radar and navigation, which is called intentional emission interference source. The other part is the completion of its own function, accompanied by the generation of electromagnetic energy emission, such as traffic vehicles, overhead transmission lines, lighting equipment, electric machinery, household appliances and industrial, medical RF equipment and so on. Therefore, this part becomes unintentional emission interference source.

1.2, from the electromagnetic interference attributes, can be divided into functional interference sources and non-functional new sources of interference.

The functional interference source refers to the direct interference of other equipment in the process of realizing the function of the equipment;

The non-functional interference source refers to the side effects that the power device produces or attaches when it realizes its own function, such as the arc discharge disturbance caused by the switch closing or cutting off.

1.3, from the electromagnetic interference signal spectrum width, can be divided into broadband interference source and narrowband interference source.

They are distinguished by the large or small bandwidth of the specified receptor.

The bandwidth of the interference signal is larger than the bandwidth of the specified receptor, which is known as narrowband interference source.

1.4, from the frequency range of the interference signal to divide

Interference sources can be divided into power frequency and audio interference source (50Hz and its harmonics), very low frequency interference source (30HZ), carrier frequency interference source (10khz~300khz), radio frequency and video interference source (300kHz), microwave interference source (300mhz~100ghz).

2, electromagnetic harassment transmission way

There are two kinds of methods of electromagnetic interference transmission: conduction coupling and radiation coupling.

The conduction transmission must have a complete circuit connection between the interference source and the sensor, and the interfering signal is transmitted along the connecting circuit to the sensor, and the disturbance occurs. This transmission circuit may include conductors, conductive components of the equipment, power supply, public impedance, grounding plates, resistors, inductors, capacitors and mutual inductance components.

The radiative transmission is transmitted through the medium in the form of electromagnetic wave, and the disturbance energy is emitted to the surrounding space by the law of electromagnetic field. The common radiation coupling consists of three kinds: 1. The electromagnetic wave emitted by a antenna is accidentally accepted by B antenna, which is called antenna-to-antenna coupling; 2. The Space electromagnetic field is induced by the wire and is coupled, called field-to-line coupling; 3. Two high frequency signal induction between parallel conductors, called wire-to-wire inductive coupling.

In practical engineering, interference between two devices usually involves coupling of many ways. Because of the simultaneous existence of multiple ways of coupling, repeated cross-coupling, together to produce interference, so that electromagnetic interference becomes difficult to control.

3. Sensitive Equipment

A sensitive device is a generic term for interfering objects, which can be a small component or a circuit board component, or a single electrical device or even a large system.

EMI inspection projects include:

1. Conduction (CE) (150khz~108mhz);
2. Intermittent interference voltage (clicks) (150kHz, 500kHz, 1.4MHz and 30MHz);
3. Interference Power (30mhz~300mhz)
4. Harmonic current (2~40 harmonics)
5. Radiation emission (RE) (100k~2.7g)

ems--

The EMS inspection items are:

1. Anti-disturbance of electrostatic discharge;
2. Radiated electromagnetic field (80mhz~1000 MHz) immunity;.
3. Electrical fast Transient/impulse group immunity;
4. Surge (lightning) immunity;
5. Injection current (150khz~230mhz) immunity;
6. Voltage SAG and short-time interrupt immunity

Emc--electro magnetic compatibility Electromagnetic compatibility

definition: refers to the ability of a device or system to operate in an electromagnetic environment that meets the requirements and does not produce an intolerable electromagnetic interference in any equipment in its environment.

Therefore, EMC includes two requirements: on the one hand, the equipment in the normal operation of the environment generated by the electromagnetic interference can not exceed a certain limit value;

On the other hand, the device has a certain degree of immunity to electromagnetic interference in the environment in which it exists.

Electromagnetic Compatibility design:

For the product to have good electromagnetic compatibility, the need to specifically consider the electromagnetic compatibility-related design content:

　　Ground design

　　Many electromagnetic interference problems are generated by the ground, because the ground potential is the entire circuit work benchmark potential, if the ground design is improper, the ground potential will be unstable, will lead to circuit failure. The purpose of the ground design is to ensure that the ground potential is as stable as possible, thus eliminating interference

　　PCB Design

　　The circuit board is the core of the problem regardless of whether the device generates electromagnetic interference or is affected by external interference or the circuit is interfering with each other. Therefore, it is of great significance to design the circuit board to ensure the electromagnetic compatibility of the equipment. The purpose of circuit board design is to reduce the electromagnetic radiation generated on the circuit board and sensitivity to external interference, reducing the interaction between the circuit board.

　　Filter design

　　For any design, filtering is one of the key technologies to solve electromagnetic interference. Because of the high efficiency of receiving and radiating antennas in the equipment. As a result, most of the radiation emitted by the device is achieved through a variety of wires, and external disturbances are often first received by the wire and then passed into the device. The purpose of the filter is to eliminate these interference signals on the wire, to prevent the interference signal conduction wire in the circuit, with the help of wire radiation, and also to prevent the transmission of the interference signal received by the wire into the circuit.

　　Shielding and lap-up design

　　For most devices, masking is necessary. Especially with the increasing frequency of circuit work, relying on circuit board design often can not meet the requirements of electromagnetic compatibility standards. The shielding design of the chassis is different from the traditional structure design, and it is difficult to add the shielding effect to the chassis if the electromagnetic shielding requirement is not considered in the structure design. Therefore, for modern electronic product design, we must consider the shielding problem from the beginning.

　　

difference

EMS (Electro magnetic susceptibility) literal translation is "electromagnetic sensitivity." It means the degree of ease of performance degradation due to electromagnetic energy. To be easy to understand, we compare electronic devices to people, the electromagnetic energy than do the cold virus, sensitivity is whether it is prone to colds. If not easy to catch a cold, the strong immunity, that is, the English word immunity, that is strong anti-electromagnetic interference.

EMC (Electro magnetic compatibility) is the literal translation of "Electromagnetic compatibility." This means that the electromagnetic energy generated by the device is not capable of interfering with other devices or the electromagnetic energy of other devices.

The term EMC has a very broad meaning. Like elephant, what you touch is a lot different from the actual one. In particular, electromagnetic phenomena, contrary to design intent, should be seen as an EMC issue.

Electromagnetic energy detection, anti-electromagnetic interference test, statistical processing of test results, electromagnetic energy radiation suppression technology, lightning and geomagnetic and other natural electromagnetic phenomena, the impact of electric field on human body, electric field intensity of international standards, electromagnetic energy transmission path, the relevant standards and restrictions are included within EMC.

EMI & EMS & EMC