Correct EMI filter installation is very important for its adequate performance.
1. For safety reasons and to make sure filters reliability, they must be mounted on the frame or chassis of the equipment, and try to shorten the earth wire, also the ground point of filter should be exact the same of equipment chassis, as shown in figure1.
Figure1 Ground point of EMI filter
If the ground point of filter and equipment chassis is not the same, the leakage current and noise current of filter go through the two points will constitute a current loop, the current loop noise will disturb other parts inside the equipment.
Besides, the earth wire of filter will introduce inductance which could worsen the high frequency attenuation characteristics of filter. So the metal case of the filter should be directly connected with equipment chassis. If the metal case of the filter is painted, the coating must be scraped off. If the metal case of filter cannot be directly grounded or using plastic cover, its grounding wire should be as short as possible.
2. Filters should be mounted at the input end of equipment power line with the wire as short as possible. Internal power supply of equipment should be connected with filter output end. If the filter input line inside the equipment is too long, the conducted interference introduced will coupling to other parts, as shown in figure2.
3. Keep the filter input line and output line separate. If the input line and output line are banded together or too close to each other, it will result in a loss of insertion loss at high frequency due to the coupling between the wires. If it is impossible to avoid the input and output line too close, twisted-pair or shielded wire must be adopted.
4. If the device is composed of several units, make sure to correctly install the filter within each unit. If some units with separate power supply are installed in the same frame, then each unit must be taken as a separate parts of the equipment. And each unit must be equipped with an adequate filter, otherwise the interference of every unit within the frame will affect other units, as shown in figure 3.