Since there are often a large number of electrical and magnetic interference sources at the production site, they can damage the normal operation of sensors, computers and even the entire inspection system. Therefore, anti-jamming technology is an important part of the sensor detection system. For those engaged in automatic inspection work, It is very necessary to understand anti-jamming technology.
A useless signal appearing in the circuit of an electronic measuring device is called noise. When noise affects the normal operation of the circuit, the noise is called interference. The formation of interference during signal transmission must have three factors, namely the interference source, the interference path and the receiving circuit with high sensitivity to noise. Therefore, the method of eliminating or attenuating noise interference can take measures against any of the three items. A more common method in the sensor detection circuit is to take corresponding measures on the interference path and the receiving circuit to eliminate or attenuate the noise interference. The following describes several commonly used and effective anti-interference techniques.
4, low frequency magnetic shielding
If the interference is a low-frequency magnetic field, the eddy current phenomenon is not obvious at this time. The anti-interference effect is not so good only by the above method. Therefore, it is necessary to use a high magnetic permeability material as a shielding layer to limit the low-frequency interference magnetic sensing line to the magnetic field. The inside of the magnetic shield is very small. Protect the protected circuit from low frequency magnetic field coupling interference. This shielding method is generally referred to as low frequency magnetic shielding. The metal housing of the sensor inspection instrument acts as a low frequency magnetic shield. If it is further grounded, it will also function as electrostatic shielding and electromagnetic shielding.
Based on the above three commonly used shielding technologies, a composite shielded cable can be used on the side where the interference is relatively serious, that is, the outer layer is a low frequency magnetic shield layer. The inner layer is an electromagnetic shielding layer. Achieve double shielding. For example, the capacitive sensor's parasitic capacitance is a key problem that must be solved in actual measurement, otherwise its transmission efficiency and sensitivity will be low. The sensor must be electrostatically shielded, and the electrode lead-out wire is double-shielded. It is generally called drive cable technology. In this way, the parasitic capacitance of the sensor during use can be effectively overcome.
