The suppression of electromagnetic interference is based on an exact analysis of the interference. The content of the analysis should include the source, nature, propagation path, coupling method, and the form of the sensor circuit, the circuit that receives the interference, and so on. The basic method of suppressing interference is to take measures from the "three elements" of forming interference, in terms of noise sources, coupling channels and interference receiving circuits.
1. Eliminating or suppressing noise sources Eliminating or suppressing noise sources is the most proactive measure because it can fundamentally eliminate or reduce interference. In actual work, only a part of the noise source within the designer's management authority can be eliminated or suppressed; and most noise sources are independent and cannot be eliminated or suppressed, such as natural noise sources, electrical equipment generated by surrounding factories. Noise and so on. In this case, the sensor circuit is considered as noise, and the other device is a useful signal, and such a signal cannot be suppressed. In summary, there are limits to the way to eliminate or suppress noise sources.
2. The coupling channel that disrupts the interference of the coupled channel interference, that is, the transmission mode can be divided into two categories, one is in the form of "road" and the other is in the form of "field". Different countermeasures can be used for interference with different forms of transmission.
(1) For interference in the form of "road", interception or low-impedance path can be used to prevent interference from entering the receiving circuit. For example, the insulation resistance is increased to suppress leakage interference; the isolation technology is used to cut off the ground loop interference; the filtering, shielding, grounding and other technologies are used to give the interference a low-resistance path, and the interference is led; the shaping, limiting, etc. are used to cut off the digital signal interference. Ways, etc.
(2) For the interference in the form of "field", the shielding measures are generally used and the "channel" suppression interference measures are used together, so that the interference is blocked and it is difficult to invade the circuit in the form of "road".
3. Eliminate the sensitivity of the receiving circuit to interference. Different circuit structure forms have different sensitivity (ie sensitivity) to interference. Generally, a high input impedance circuit is more susceptible to interference than a low input impedance circuit; an analog circuit is more susceptible to receiving interference than a digital circuit. In order to weaken the sensitivity of the circuit to interference, filtering, frequency selection, twisted pair, symmetrical circuit and negative feedback can be used.
4, using software to suppress interference for some of the interference that has entered the circuit, hardware measures are not easy to achieve or not easy to work, you can consider in the intelligent sensor circuit using the microprocessor, by programming a certain program for signal processing and analysis and judgment, To achieve the purpose of suppressing interference.
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