Four anti-interference technical measures for sensors
The sensor anti-jamming technical measures are as follows:
First, shielding technology
Including electrostatic shielding, electromagnetic shielding, low frequency magnetic shielding, thermal shielding, etc.
1. Electrostatic shielding: Electrostatic shielding is to use copper or aluminum and other conductive metals as materials to make a closed metal container, and connect it to the ground wire, put the circuit that needs to be shielded in it, so that the electric field of the external interference electric field is not Affecting the internal circuit, in turn, the power line generated by the internal circuit cannot escape to affect the external circuit. Electrostatic shielding can not only prevent electrostatic interference, but also prevent the interference of alternating electric fields, so the shell of many instruments is made of conductive material and grounded. Although more and more instruments are made of engineering plastics (ABS) for the case, when you open the case, you will still see a layer of grounded metal film stuck on the inner wall of the case, which acts like a metal case Static shielding effect.
2. Low-frequency magnetic shielding: low-frequency magnetic shielding is an effective measure used to isolate low-frequency magnetic field and fixed magnetic field coupling interference. There is a magnetic field around any wire or coil passing current, and there is an objective magnetic field. They may cause magnetic field coupling interference to the signal line of the detection instrument or the instrument. In order to prevent magnetic field coupling interference, high magnetic permeability material must be used as the shielding layer, so that low-frequency interference magnetic field lines pass through the magnetic shielding layer with low magnetic resistance, so that the circuits inside the low-frequency magnetic shielding layer are protected from low-frequency magnetic field coupling interference. For example, the metal shell of the instrument acts as a low-frequency magnetic shield. If the shell is further grounded, it can also play the role of electrostatic shielding.
3. Electromagnetic shielding: electromagnetic shielding is also made of metal with good conductivity to make different shapes such as shielding cover and shielding box, which surrounds the protected circuit. The interference object it shields is not an electric field, but a high-frequency (above 40KHz) magnetic field. When the high-frequency magnetic field generated by the interference source encounters a well-conducting electromagnetic shielding layer, an eddy current of the same frequency is induced on its outer surface, thereby consuming the energy of high-frequency interference. Secondly, the eddy current will also generate a new magnetic field. According to Lenz’s law, its direction is exactly opposite to the direction of the interference source to offset part of the energy of the interference magnetic field, thereby protecting the circuit inside the electromagnetic shielding layer from high-frequency interference magnetic fields. Impact.
Because the nature of radio broadcasting is electromagnetic waves, electromagnetic shielding can also absorb their energy. This is that we cannot receive the radio in the car (steel body, but not grounded), and we must pull the antenna of the radio out of the car. the reason.
If the electromagnetic shielding layer is grounded, it can also have the function of electrostatic shielding, and the shielding effect on electromagnetic waves is better. The copper mesh shielded cable usually used as a transmission line can simultaneously play the role of electromagnetic shielding and electrostatic shielding when grounded.
