When selecting filter, we should pay attention to the following points:
(1) make clear the working frequency and the interference frequency to be suppressed, if the two are very close, we need to apply the very steep frequency characteristic filter to separate the two kinds of frequency;
(2) to ensure that the filter can work reliably at high voltage;
(3) when the filter passes the maximum rated current, its temperature rise is low, so as to ensure that the working performance of the components in the filter is not destroyed when the rated current is continuously working;
(4) in order for the frequency characteristic of the filter to be in accordance with the design value, it is required that the value of the impedance of the signal source and the impedance of the load connected to the filter be equal to the specified value at the time of the design;
(5) the filter must have a shielding structure, Shielding box cover and body to have good electrical contact, filter capacitor lead should be as short as possible, it is best to use short lead low inductance through the core capacitance; (6) it is necessary to have high working reliability because the fault of filter used for electromagnetic interference protection is often more difficult to find than that of other components.
Attention should be paid to the following points when installing the filter:
(1) the power line filter should be installed as close as possible to the power source entrance of the equipment, and the unfiltered power cord should not be circuitous in the device frame;
(2) Capacitor leads in filters should be as short as possible to avoid resonance at lower frequencies due to lead reactance and capacitive reactance;
(3) there is a large short-circuit current passing through the grounding conductor of the filter, which will cause additional electromagnetic radiation, so the filter element itself should be shielded and grounded;
(4) the input line and output line of the filter can not cross, otherwise the crosstalk will be caused by the input and output capacitive coupling path of the filter, thus reducing the filter characteristic. The usual method is to add a partition or shield layer between the input and output terminals.