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EFT test methods and principles applied interference
Release time:2014-12-22   Click times:17590

When EFT test with L1, L2, L3, N and PE and other ports. PE and earth are two concepts, electrical fast pulse interference is common mode properties, provided in the standard experiment setup can be seen from the figure the test signal generator to the cable core through the choice of the coupling capacitor to the corresponding power line (L1, L2, L3, N and PE), the signal cable shield and the coupling / decoupling network is connected to the chassis when the machine EFT test with L1, L2, L3, N and PE and other ports. PE and earth are two concepts, electrical fast pulse interference is common mode properties, provided in the standard experiment setup can be seen from the figure the test signal generator to the cable core through the choice of the coupling capacitor to the corresponding power line (L1, L2, L3, N and PE), the signal cable shield and the coupling / decoupling network is connected to the chassis, the chassis is connected to the reference ground terminal.

????This indicates that burst interference is actually applied between the power line and the reference earth, so add the power line interference is common mode interference and for the use of experimental coupled folder, the electrical fast pulse through the coupling plate distributed capacitance between the cable into the test cable test, and the test cable to the received pulse is still relatively reference for the ground plane.

??????Accordingly, by coupling the test cable clamp interference is still applied common mode nature. Determine the nature of the disturbance, then we can take the appropriate measures to make the device successfully passed experiments. So we can see that power filter used in the X capacitor (differential mode capacitor) for EFT interference is no inhibition.
??????If the device is a metal shell, Y capacitors (common mode capacitor) will work, high frequency bypass EFT to the housing top, and then back to the source device via the distributed capacitance between the housing and the reference ground, so as not to enter the circuit.
????Mechanism electrical fast pulse interference caused equipment failure according to foreign scholars, thereby causing equipment failure mechanism of burst disturbance, single pulse energy is small, it does not cause malfunction of the equipment. However, the interference burst signal line for charging the junction capacitance device, when the energy is accumulated to a certain extent above, it may cause the line (as well as the system) malfunction.

????Therefore, there will be a time line error process, but there will be some chance (can not guarantee how much time interval, the lines must be wrong, especially when the test voltage reaches the vicinity of the critical point). And it is difficult to judge whether it is respectively applied pulse or pulse is applied, together with the equipment easier to fail. It is difficult to conclude device for positive pulses and negative pulses which are more sensitive.
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????Practice shows that a certain piece of equipment is often a cable in a certain kind of test voltage, are particularly sensitive to a polarity. Experiments show that the signal line is much more than the power cord to electrical fast pulse interference sensitive.
????Equipment and effective measures by electrical fast pulse test First we analyze the interference injection method: EFT interference signal is a decoupling network in capacitive coupling 33nF to main power lines above by coupling (the signal or control cables through capacitive coupling clamp causing interference, the equivalent capacitance is 100pF). For 33nF capacitor, its cut-off frequency of 100K, which is the interference signal 100KHZ above can be; and 100pF capacitor, cutoff frequency is 30M, allowing only frequencies above 30MHz interference through. Interference waveform of the pulse is fast 5ns / 50ns, repetition frequency 5K, pulse duration 15ms, burst repetition period of 300ms. According to the Fourier transform, its spectrum is from 5K - 100M discrete spectral lines from each spectral line is the pulse repetition frequency.

????Know the above points, the interfering capacitive coupling plays a role in high-pass filter, because the impedance of the capacitor decreases as the frequency increases, so will not interfere with the low-frequency component is coupled to the EUT, and only the higher frequencies the interfering signal will enter the EUT. When we add in the EUT common mode inductance circuit (with particular attention to that, where common mode inductance must be added to the main power supply line and return line or reach saturation and thus interfere with the purpose of attenuation occurs) on Some can attenuate high frequency interference components, inductive impedance increases as the frequency increases. Therefore, the interference signal EUT above only the middle part of the actual frequency is applied to.

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