Grounding and housing related content of power filter
This situation is also quite common. Many engineers have poor overlap between the filter housing and the chassis when installing filters (with insulation paint); Meanwhile, the use of a longer grounding wire will result in a deterioration of the high-frequency characteristics of the filter and a decrease in filtering performance. Due to the long grounding wire, the distributed inductance of the wire cannot be ignored at high frequencies. If the filter is well overlapped, the interference signal can be directly grounded through the housing. If the connection between the filter housing and the chassis is poor, it is equivalent to a distributed capacitance between the filter housing (ground) and the chassis, which will result in a high grounding impedance of the filter at high frequencies, especially near the frequency of resonance between distributed inductance and distributed capacitance, where the grounding impedance tends to infinity. The impact of poor grounding of the filter on its performance is shown in Figure 3.
Due to poor grounding of the filter and high grounding impedance, some disturbance signals can pass through the filter. To solve the problem of poor overlap, the insulation paint on the chassis should be scraped off to ensure a good electrical connection between the filter housing and the chassis.
In this installation method, the housing of the filter is in good contact with the chassis, blocking the opening of the power cord on the chassis and improving the shielding performance of the chassis; In addition, the input and output lines of the filter are isolated by chassis shielding, eliminating interference coupling between the input and output lines and ensuring the filtering performance of the filter.
The installation method of the filter directly affects its filtering effect. In order to fully utilize the performance of the filter, the following principles should be followed when installing the filter:
1) Install near the power inlet, preferably covering the power cord inlet hole on the chassis with a filter housing, as shown in Figure 4;
2) The shorter the grounding wire, the better;
3) The filter housing is well overlapped with the chassis;
4) The input and output lines of the filter are separated and cannot be parallel or crossed;
5) Avoid strong interference sources near the filter.
Example of installation of power filter
The experimental results show that, on the one hand, based on the existing electromagnetic pulse simulator, a pulse electric field that meets the calibration requirements can be generated. In the experiment, the waveform measured by the electric field sensor is consistent with the waveform measured by the load voltage of the simulator. Using a voltage divider to measure the voltage can obtain the electric field inside the standard device; On the other hand, the consistency of calibration data obtained from different calibration devices is good. The impact of sensor placement on field uniformity was not considered in this study, and will be further evaluated in the next step of research.
