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Interference Way for Group Pules Generator Test

When having group pulse generator test, there are L1, L2, L3, N and PE etc port. PE and the earth are two different concepts, the nature of electronic rapid pulse disturbance is common mode, in standard available experimental Settings figure can be seen from the test of the signal generator to cable core through the selection of the coupling capacitance added to the corresponding power cords (L1 and L2, L3, N and PE), signal cable shielding layer is a roll of the shell and the coupling decoupling network connected, the cabinet is received reference on ground terminal.

This shows that pulse group of interference is actually added between the power cord and reference earth, so the interference is added in the power cord is common mode interference, however, to the coupling clip experimental way, the rapid pulse will go into the cable through the capacitance between the coupling board and cable, and the pulse that the cable received is based on relatively reference for pick up the floor.

Therefore, the nature of interference that through the coupling clip on anti-deflagration cable is still common mode. After the nature of the interference confirmed, we can take corresponding measures to make equipment smoothly through the experiment. So we can easily see that power supply filter used in the X capacitance (differential mode capacitance) has no suppression for EFT interference.

If the equipment has metal shell, Y capacitance (common mode capacitors) will work, the high frequency EFT will be bypassed to shell, then back to the signal source through the capacitance between equipment shell and reference earth, and not enter into the circuit.

The electronical rapid pulse disturbance lead to equipment failure mechanism, based on the research of the mechanism of equipment failure caused by interference from foreign scholars to pulse group, a single pulse with less energy, will not have equipment malfunction. But pulse jamming signal line of equipment charge capacitance, when the above energy accumulated to a certain degree, that may cause the line (and even system) of the wrong action.

Therefore, the line error will have a process time, and can have certain contingency ( no guarantee about the time interval that the line error, especially when test voltage is at the critical point nearby). And it is difficult to judge in which way the equipment is easier to failure, be applied respectively pulse or put together pulse. Also difficult to judge in which situation the equipment is more sensitive, positive or negative pulses.

The practice shows that a device is often sensitive to a polarity of any particular one cable in a certain test voltage. Experiments show that, signal lines are much more sensitive to electric rapid pulse than power line.

The effective measures of equipment tested by the rapid pulse. First we analyze the interference injection patterns: EFT interfering signal is formed by 33nF capacity that coupled the decoupling network coupled to the main power cord (however, signal or control cable is through EFTC, equivalent capacitance is 100 pF). For the capacity of 33nF, its cut-off frequency is 100 K, in other words, interference signal above 100 KHZ can through. And the capacity of 100pF, the cut-off frequency is 30 M, allowing only above 30 MHz frequency interference through. The rapid pulse interfering waveform is 5 ns / 50 ns, repeat frequency is 5 K, pulse duration is 15 ms, pulse repeat cycle is 300 ms. According to Fourier transform, its spectrum from 5 K-100 M is a discrete lines, the distance of each spectral line is frequency of pulse repetition.

From the above, the interference coupling capacitance plays a high-pass filter role, because the impedance of the capacitor will drop when frequency increases, so low frequency components of the interference will not be coupled to the EUT. Only higher frequency interference signals will enter into EUT. When we add common-mode inductor to EUT circuit (special attention should be paid is that the common mode inductance must be added in the main power or its back online, or else there may be an saturated and can not reach the purpose of attenuation interference) it can attenuate some high frequency interference composition, because the impedance of the inductance will increase when the frequency increase. Therefore, actual applied to the EUT disturbance signal of the above is only part of the middle frequency.

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