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2022
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What is the difference between electromagnetic disturbance and electromagnetic interference?
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Electromagnetic harassment and electromagnetic interference are terms we often hear, so what is their connection? What is the difference? Today, VIP Electronics will discuss with you.
1. The meaning of electromagnetic disturbance and electromagnetic interference
Electromagnetic harassment
We say that any electromagnetic phenomenon that may cause the performance of devices, equipment or systems to degrade or cause damage to living or inanimate matter can be collectively referred to as electromagnetic disturbances. Electromagnetic disturbances may be electromagnetic noise and unwanted signals or changes in the transmission medium itself.
Electromagnetic Interference
Electromagnetic interference is the degradation of equipment, transmission channel or system performance caused by electromagnetic disturbance. In fact, electromagnetic harassment is just an electromagnetic phenomenon, that is, it is a physical phenomenon that exists objectively, and electromagnetic harassment may cause degradation or damage, but it does not necessarily have actual consequences. So, in essence, electromagnetic interference is the consequence of electromagnetic disturbance.
2. Where does electromagnetic harassment occur?
Generally speaking, electromagnetic disturbance often occurs in high-speed digital signal lines, switching circuits, pulse generating circuits and high-power control circuits.
Circuits, etc., where the voltage and current change rapidly in a very short period of time, and where the circuits containing inductance and capacitance are turned on and off. In addition, when the magnetic field, electric field, electric charge and other electricity changes rapidly, electromagnetic disturbance will also occur.
3. What is the principle of electromagnetic disturbance?
In a switching circuit, the shorter the voltage/current increase or decay time t, the wider the noise bandwidth. rapidly changing
The greater the amplitude of the voltage V and the current I, the greater the amplitude of the noise.
It is worth noting that in a circuit with an inductive load, it is easy to generate intermittent electromagnetic interference at the moment when the circuit is switched from on to off. In fact, the noise waveform gradually increases from small to large, which also corresponds to the process of the distance between the switch contacts from small to large.
In the circuit, when the DC voltage VD generates a current I on the load connected in series with L and R, the moment the switch S is switched from on to off, a voltage of the opposite polarity is generated at both ends of L that is dozens of times larger than VD, sometimes hundreds of times. The spike voltage (called the inductor kickback voltage).
When there is a parasitic capacitance C0 at both ends of L, the following phenomena will occur:
When C0=100pF, it will generate about -848V, 225kHZ oscillation;
When C0 can be ignored, it will reach -6000V;
The larger the parasitic capacitance, the lower the voltage across the inductor and the lower the oscillation frequency.
In the actual circuit, even if a capacitor is connected at both ends of the inductor L, due to the influence of the lead inductance of the capacitor, the best effect of the capacitor will not be obtained.
Capacitors must be high-voltage resistant, otherwise they may be damaged. A circuit that ignites a fluorescent lamp using the high voltage generated across the ballast. Once the oscillating high voltage generated by it is transmitted to other electrical equipment, it will become a disturbance.
VIP Xiaobian summarizes for you that electromagnetic interference refers to the consequences that can cause performance degradation, and electromagnetic disturbance refers to objective phenomena that can cause such performance degradation. Electromagnetic disturbance only constitutes electromagnetic interference when it affects the normal operation of sensitive equipment. Therefore, electromagnetic disturbance is the cause, and electromagnetic interference is the result.
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