Common terms of electromagnetic compatibility

EMC mainly studies how to make all kinds of electrical and electronic equipment and components working in the same electromagnetic environment work normally , Mutual interference , Compatibility status reached . EMC research is mainly aimed at electrical and electronic equipment , It also involves electrostatic discharge in production 、 The influence of electromagnetic radiation on human body .

1、 Electromagnetic disturbance and electromagnetic interference

Electromagnetic disturbance refers to anything that may cause equipment performance degradation or damage to living substances Electromagnetic phenomena .

Electromagnetic disturbance caused by electromechanical or other artificial devices , It is called artificial harassment ; Electromagnetic disturbance from natural phenomena , Called natural harassment .

Electromagnetic interference refers to the degradation of equipment or transmission channel performance caused by electromagnetic disturbance .

So the meaning of harassment and interference is different . conceptually , Disturbance is a kind of electromagnetic energy , Disturbance is the result or consequence of disturbance .

Electromagnetic interference is generated from the disturbance source ; The existence of a large number of disturbance sources causes electromagnetic environmental pollution , Leading to the sharpening of electromagnetic compatibility problems . Mainly in ：

The total number of electronic devices working at the same time is increasing , The number of electronic devices per 4~5 Double the number of years ;

The power of the transmitter is increasing , For example, the transmitted pulse power of some radars reaches tens or even hundreds of megawatts ;

Many radio bands are seriously overloaded , As a result, the same frequency band has to be used repeatedly for different types of electronic equipment ;

The level of electromagnetic disturbance generated by electronic equipment during operation continues to increase . For example, the interference level generated by the operation of some medical equipment can reach hundreds of volts per meter .

Electromagnetic disturbance only affects the normal operation of sensitive equipment , Electromagnetic interference . Electromagnetic interference refers to the consequences that can cause performance degradation . Electromagnetic disturbance refers to the objective phenomenon that can cause such performance degradation . summary ： Electromagnetic disturbance is the cause , Electromagnetic interference is the result .

Electromagnetic disturbance is just an electromagnetic phenomenon , That is, an objective physical phenomenon , It may cause degradation or damage , But it doesn't have to have consequences . Electromagnetic interference is caused by electromagnetic disturbance consequence . 

What is the occasion of electromagnetic disturbance , And how it came about . 

Electromagnetic disturbance usually occurs in the following situations ： High speed digital signal line 、 Switch circuit 、 Pulse generation circuit and high-power control circuit, etc. in a very short time, the voltage and current change rapidly , The occasion when the circuit containing inductance and capacitance is on and off .  The magnetic field 、 The electric field 、 When the electric charge changes rapidly , Also produce electromagnetic disturbance . 

In the circuit of switch action , voltage / Increase or decrease time of current t Shorter , The wider the bandwidth of the noise ; Rapidly changing voltage V And current I The greater the amplitude of , The greater the amplitude of the noise . 

Especially in the circuit of inductive load , The instant a circuit changes from on to off , It is easy to produce intermittent electromagnetic interference .

The noise waveform changes from small to large , This corresponds to the process of the distance between switch contacts from small to large . 

In the circuit , DC voltage VD stay L and R A load connected in series generates a current I when , switch S The instant of switching from on to off , stay L The two ends produce a ratio VD Dozens of times larger 、 Sometimes hundreds of times the peak voltage of opposite polarity （ It is called the inductive recoil voltage ）. 

When L Parasitic capacitance at both ends C0 when , There will be the following phenomena ： 

When C0=100pF when , Produce about - 848V,225kHZ Oscillation of ; 

When C0 When it can be ignored , Will arrive at - 6000V; 

The greater the parasitic capacitance , The lower the voltage across the inductor , The lower the oscillation frequency . 

In actual circuits , Even in inductance L Connect capacitors at both ends , Because of the influence of capacitor lead inductance , Will not get the most correct effect of the capacitor , Attenuate the falling part of the vibration waveform dυ/dt Bigger , The high frequency part is left . 

The capacitor must be high voltage resistant , Otherwise it may be destroyed . A circuit that uses the high voltage generated at both ends of the ballast to ignite the fluorescent lamp . Once the oscillating high voltage generated by it is transmitted to other electrical equipment , The old will become harassment . 

2、 Electromagnetic compatibility (EMC-Electromagnetic Compatibility）

Failure or performance degradation of electronic equipment due to electromagnetic disturbance , It is called that the equipment is sensitive to electromagnetic disturbance . How to seek a harmonious relationship and coexistence conditions between equipment and electromagnetic environment , This is electromagnetic compatibility technology .

Common terms of electromagnetic compatibility

To describe electromagnetic disturbance and electromagnetic compatibility , Many terms need to be introduced , National military standards GJB72-85《 Terminology of electromagnetic interference and electromagnetic compatibility 》 A book has detailed content , Here we only select some of them to introduce to you .

Electromagnetic compatibility EMC（Electromagnetic Compatibility）

The coexistence state in which devices can perform their respective functions together in a common electromagnetic environment , That is to say, the equipment will not be degraded due to electromagnetic emission of other equipment in the same electromagnetic environment ; It will not degrade other equipment in the same electromagnetic environment due to its electromagnetic emission .

Common terms of electromagnetic compatibility

To describe electromagnetic disturbance and electromagnetic compatibility , Many terms need to be introduced , National military standards GJB72-85《 Terminology of electromagnetic interference and electromagnetic compatibility 》 A book has detailed content , Here we only select some of them to introduce to you .

Electromagnetic compatibility EMC（Electromagnetic Compatibility）

The coexistence state in which devices can perform their respective functions together in a common electromagnetic environment , That is to say, the equipment will not be degraded due to electromagnetic emission of other equipment in the same electromagnetic environment ; It will not degrade other equipment in the same electromagnetic environment due to its electromagnetic emission .

electromagnetic interference EMI（Electromagnetic Interference)

Electromagnetic disturbance leads to the interaction of electronic equipment , An electromagnetic phenomenon that causes adverse consequences .

Radiation emission RE (Radiated Emission)

Spread through space 、 Useful or unwanted electromagnetic energy .

Conducted emission CE (Conducted Emission)

Electromagnetic emission transmitted along a power or signal line .

Electromagnetic sensitivity EMS（Electromagnetic Susceptibility)

Undesired response of equipment exposed to electromagnetic environment . That is, the measurement of the sensitivity of the equipment to the surrounding electromagnetic environment . Electromagnetic sensitivity means that the electromagnetic environment has caused the degradation of equipment performance .

Radiation sensitivity RS（Radiated Susceptibility)

Measurement of the radiation disturbance field causing degradation of equipment performance .

Conduction sensitivity CS（Conducted Susceptibility)

When the equipment performance is degraded , Measurement of the disturbance signal current or voltage introduced from the conduction mode .

（Electromagnetic Interference)

Electromagnetic disturbance leads to the interaction of electronic equipment , An electromagnetic phenomenon that causes adverse consequences .

Radiation emission RE (Radiated Emission)

Spread through space 、 Useful or unwanted electromagnetic energy .

Conducted emission CE (Conducted Emission)

Electromagnetic emission transmitted along a power or signal line .

Electromagnetic sensitivity EMS（Electromagnetic Susceptibility)

Undesired response of equipment exposed to electromagnetic environment . That is, the measurement of the sensitivity of the equipment to the surrounding electromagnetic environment . Electromagnetic sensitivity means that the electromagnetic environment has caused the degradation of equipment performance .

Radiation sensitivity RS（Radiated Susceptibility)

Measurement of the radiation disturbance field causing degradation of equipment performance .

Conduction sensitivity CS（Conducted Susceptibility)

When the equipment performance is degraded , Measurement of the disturbance signal current or voltage introduced from the conduction mode .

3、 Three elements of electromagnetic interference

Electromagnetic disturbance source , It refers to the components that generate electromagnetic disturbance 、 device 、 Equipment or natural phenomena ;

Coupling path or coupling channel , It refers to coupling energy from disturbance source to sensitive equipment , The medium that causes the device to respond ;

Sensitive equipment , It refers to the equipment responding to electromagnetic disturbance .

The three elements of EMC are indispensable in the analysis of EMC , Any element is missing , The process of electromagnetic interference will not happen , It is very helpful for us to clarify the electromagnetic interference of complex systems . In terms of power supply , It usually plays the role of interference source in the system , We usually improve the interference of power supply to external devices or systems from the perspective of the first two factors .

  Reference documents ：

Brief tutorial on electromagnetic compatibility （1）