Radiation emission exceeding the standard (there are two possibilities for equipment to emit radiation disturbance exceeding the standard)
One is the imperfect shielding performance of the equipment housing; the other is the escape of radio frequency disturbance through power lines and other cables. If there is no sign of improvement, it should be suspected that the shielding performance of the equipment housing is not perfect; if there is any improvement, it may be a cable problem. If the necessary measures are taken against the above two possibilities, there is still no improvement. It may just be the problem of the remaining cables on the equipment.
2. Conducted disturbance emission exceeded the standard (equipment's conducted disturbance emission exceeded the standard, mainly due to cable problems, but the frequency of exceeding the standard is usually relatively low, which is often troublesome to handle).
(1) Processing of power lines
(1) Check whether there is a signal cable near the power line. It is possible that the coupling between the signal cable and the power line uses the conducted disturbance of the power line to transmit beyond the standard (this situation is more common in the case of high frequency band). If, or widen the distance between the two capitals, or use shielding measures;
(2) Install power line filters (if there are already filters, then switch to high-performance filters). Pay special attention to the installation location (as far as possible on the power line entrance end of the chassis) and installation conditions, to ensure that the filter housing and chassis overlap well and grounding well;
(3) Although measures have been taken, the conducted disturbance emission of equipment has not yet reached the standard (especially in the low frequency band). At this point, it is considered to connect an inductor in series where the line inside the device connects to the ground terminal. Because this part of the connection is single-point grounded, there is no current flowing normally, so this inductor may be done very large, without worrying about the saturation of the iron core. The reason for taking this measure is that the conductive disturbance emission test of equipment is actually a common-mode voltage test (disturbance voltage test of power line to the earth). There is working current flowing through the power line. Therefore, the filter inductance value of the filter is limited by the working current and can not be done very much. The insertion loss of the filter is also limited. Not that the loss of the low frequency end is more limited. The additional inductance in the new scheme can make up for this shortcoming and obtain better suppression ability of conduction disturbance.
(2) Processing of signal lines
(1) Pay attention to whether there is any other radiation energy around the signal line (the nearby wiring and the layout of the printed board) being led to the signal line. If there is, or widen the distance between the two capitals, or use shielding measures, or consider changing the internal layout of equipment and the layout of printed boards;
(2) Ferrite magnetic ring (or ferrite magnetic clamp) is set on the signal line;
(3) Common-mode filtering is applied to the signal line, and filter connector (or filter array board) is used when necessary. Attention should be paid to the parameters of the filter. The frequency of conduction disturbance emission exceeding the standard is lower than that of radiation disturbance emission exceeding the standard.
3. Electrical Fast Pulse Group Interference
From the original intention of the pulse group test, the common mode interference test is mainly carried out, but the waveform of the interference pulse is very steep and the duration is very short, so it contains extremely rich high frequency components, which leads to some interference escaping from the transmission cable in the process of the interference waveform transmission. The combined interference of conduction and radiation eventually occurs.
For the interference of pulse group, filter (power and signal line filtering) and absorption (ferrite core absorption) are mainly used. The placement of ferrite cores means that the position of ferrite cores should not be changed at will in the future, because we have repeatedly stressed that the pulse group interference is not only a conductive interference, but also contains radiation components. The radiation interference escapes from different locations are different. Elusive. Ferrite cores are generally most effective at the source of interference and at the entrance of equipment.
4. Unqualified surge anti-interference test
The biggest characteristic of lightning surge test is that the energy is very large, so the scheme of using ordinary filter and ferrite core to filter and absorb surge is basically ineffective. It is necessary to use special surge absorption devices such as gas discharge tube, varistor, silicon transient voltage absorption diode and semiconductor discharge tube.
There are two kinds of lightning surge tests, common mode and differential mode. Because of the use of some surge absorbers, the corresponding situation with the test should be taken into account. In order to show the effect of operation, surge absorbers should be used at the inlet of the line. Because the di/dt of the surge absorbed species is very large, no signal line and power line can pass near the device to prevent interference from introducing into the signal and power line due to electromagnetic coupling. In addition, the pins of the surge absorber should be short, and the absorption capacity of the absorber should be matched with the surge voltage and the test level of the power supply.
Finally, the combination protection scheme will give full play to the respective characteristics of different protection devices, so as to achieve the best protection effect.