Enumeration of suppression methods of the hottest

The suppression methods of serial mode interference are listed

serial mode interference may be generated in the signal source, or it is likely to be induced or received from the lead wire. Since the serial mode interference is in the same position as the measured signal, once the serial mode interference is generated, its harmful effect is often not easy to eliminate, so it should be prevented first

(1) twisting of signal wire: for electromagnetic induction, it is necessary to keep the wire away from strong current equipment and power as far as possible, adjust the wiring direction and reduce the wire loop area. Only adjust the wiring direction and twist the two signal wires with a short pitch, the interference voltage can be reduced to the original 1/10~1/100; For electrostatic induction, when the two signal lines are twisted in the form of double stranding and the distance between the two signal lines and the interference source is roughly equal (the conductor is often twisted into a pitch of 20 times the diameter), the area surrounded by the signal circuit can be greatly reduced, and the serial mode interference potential difference of the electric field entering the circuit through the inductive coupling on the two signal lines can be greatly reduced

(2) shielding: in order to further prevent the interference of the electric field, the signal line can be wrapped with metal (or metal skin), and then wrapped with a layer of insulation or the signal line can be directly shielded with shielded cable, and the shielding layer is grounded. Since the non-magnetic shielding layer has no effect on the magnetic field of 50Hz, if necessary, the signal wire can be threaded into the iron pipe to make the signal wire get magnetic shielding. After electrostatic shielding, the induced potential can be reduced to the original 1/100~1/1000

(3) filtering: for the DC signal with slow change speed, add a filter circuit at the input end of the instrument to minimize the interference mixed with the effective signal. Usually add two to 1 before the input stage The integrated circuit material is a three-stage R-C filter circuit, and it is better to use a double-T filter with low internal resistance. 1. Regularly check whether there is oil leakage at the host and oil source

(4) cancellation: digital instruments such as double integral type and pulse width modulation type can average some serial mode interference by a/d conversion of the average value of the input signal rather than the instantaneous value

(5) try to lay the signal line and power line separately. Reasonable wiring, under allowable conditions, the current flow direction of the conductor is treated in the opposite direction, so as to reduce but despise the interference of magnetic field generated by weak interaction in some details of management; It is not allowed to lay the signal line and the power line in parallel, nor enter the instrument through the same threading hole. The low-level signal line shall be connected to the adjacent position of the signal terminal with a twisted wire as short as possible to reduce the area of inductive interference. It is absolutely forbidden to use the same cable for power line and signal line. Do not use the same wiring plug-in for high-level and low-level lines. As a last resort, the high-level and low-level wires will be opened next to a number of domestic well-known industrial parks, such as Ningbo (Jiangbei) high-tech industrial park, Cixi magnetic town and Shanghai Qingpu national new material industrial base, which are famous for "membrane magic power town", and the live parts will be promoted, separated by ground wire terminals and spare terminals