The use of metal materials made of containers. The need to protect the circuitry wrapped in which can effectively prevent the interference of 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 electromagnetism, placed in the electrostatic field in the confined hollow conductor internal electric field lines, its internal points of equal potential. With this principle, copper or aluminum and other conductive metal as a material, the production of closed metal containers, and connected to the ground, the need to protect the circuit value r which, so that the external interference with the electric field does not affect the internal circuit, in turn, the internal circuit generated by the electric field will not affect the external circuit. This method is called electrostatic shielding. For example, the sensing hooting measurement circuit, in the power transformer between the primary and secondary sides of a gap between the insertion of a conductor, and ground it, you can prevent the two windings of the electrostatic coupling, this method belongs to the electrostatic shielding.
3, electromagnetic shielding
For high-frequency interference with magnetic fields, the use of eddy current principle, so that high-frequency interference with electromagnetic fields in the shielding of the metal to produce eddy currents, consuming interference with the energy of the magnetic field, the eddy current magnetic field counteracts the high-frequency interference with the magnetic field, so as to protect the circuit from the impact of high-frequency electromagnetic fields. This shielding method is called electromagnetic shielding. If the electromagnetic shielding layer is grounded, and at the same time the role of electrostatic shielding. Sensor output cables generally use copper mesh shielding, both electrostatic shielding and electromagnetic shielding. Shielding materials must be selected conductive good low-resistance materials, such as copper, aluminum or silver-plated copper.
4, low-frequency magnetic shielding
Interference such as low-frequency magnetic field, the eddy current phenomenon is not too obvious, only with the above method of anti-jamming effect is not very good, so it must be used to use high permeability materials as a shielding layer, in order to limit the low-frequency interference with the magnetic susceptibility of the resistance of the magnetic shielding layer is very small. So that the protected circuits from the impact of low-frequency magnetic coupling interference. This shielding method is generally known as low-frequency magnetic shielding. Sensor detection instrument of the iron shell to play the role of low-frequency magnetic shielding. If further grounded, and at the same time the role of electrostatic shielding and electromagnetic shielding.
Based on the above three commonly used shielding techniques, so in the interference is more serious on her side, you can use composite shielding cable, that is, the outer layer is a low-frequency magnetic shielding layer. The inner layer is electromagnetic shielding layer. To achieve the role of double shielding.