What are the commonly used anti-jamming technologies for sensors?
1. shielding technology
Using metal materials to make containers. Enclosing the circuit to be protected can effectively prevent interference from electric or magnetic fields. This method is called shielding. Shielding can be divided into electrostatic shielding, electromagnetic shielding and low-frequency magnetic shielding.
2. electrostatic shielding
According to the principle of electromagnetics, there is no electric field line inside a closed hollow conductor placed in an electrostatic field, and the internal points are equipotential. Using this principle, a closed metal container is made of a metal with good conductivity such as copper or aluminum and connected to the ground wire. The value of the circuit that needs to be protected is r, so that the external interference electric field does not affect its internal circuit, and vice versa , The electric field generated by the internal circuit will not affect the external circuit. This method is called electrostatic shielding. For example, in the sensor measurement circuit, insert a conductor with a gap between the primary and secondary sides of the power transformer and ground it to prevent electrostatic coupling between the two windings. This method is classified as electrostatic shielding. .
3. electromagnetic shielding
For the high-frequency interference magnetic field, the principle of eddy current is used to make the high-frequency interference electromagnetic field generate eddy current in the shielding metal, which consumes the energy of the interference magnetic field, and the eddy current magnetic field cancels the high-frequency interference magnetic field, thereby protecting the protected circuit from the influence of the high-frequency electromagnetic field. . This shielding method is called electromagnetic shielding. If the electromagnetic shielding layer is grounded, it also serves as an electrostatic shield. The output cable of the sensor is generally shielded by copper mesh, which has the function of electrostatic shielding and electromagnetic shielding. Shielding materials must be low-resistance materials with good conductivity, such as copper, aluminum, or silver-plated copper.
4. low frequency magnetic shielding
If the interference is a low-frequency magnetic field, the eddy current phenomenon is not obvious at this time, and the anti-interference effect of the above-mentioned method is not very good. Therefore, a high-permeability material must be used as a shielding layer to limit the low-frequency interference magnetic line of induction to the magnetic field. Inside the magnetic shield with very little resistance. Protect the protected circuit from the influence of low-frequency magnetic field coupling interference. This shielding method is generally called low-frequency magnetic shielding. The iron shell of the sensor detection instrument acts as a low-frequency magnetic shield. If it is further grounded, it will act as electrostatic shielding and electromagnetic shielding at the same time.
is based on the above three commonly used shielding technologies, so in the other side where the interference is more serious, a composite shielded cable can be used, that is, the outer layer is a low-frequency magnetic shielding layer. The inner layer is an electromagnetic shielding layer. To achieve the effect of double shielding. For example, the parasitic capacitance of the capacitive sensor is a key problem that must be solved during actual measurement, otherwise its transmission efficiency and sensitivity will become lower. The sensor must be electrostatically shielded, and the electrode lead wire adopts double-layer shielding technology, which is generally called drive cable technology. This method can effectively overcome the parasitic capacitance of the sensor during use.
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