Electromagnetic interference (emi) is a variety of electromagnetic induction effects that reduce the characteristics of automatic control system equipment, transmission safety channels or system software.
The process of interference generation is that the interference signal from the interference source passes through the coupling safety channel to the interfered machine and equipment.The three stages of interference are called the three elements of interference system software, namely, the source of interference, the mode of interference propagation and the interfered equipment.
How does electromagnetic flowmeter resist interference
1. Classification of electromagnetic interference
In the industrial production measurement and control system, the interference of electromagnetic flowmeter is the key problem that endangers all normal work, its cause will exist in the system software interior, that is, suffer the interference harm caused by itself, will also come from the system software outside, that is, suffer the harm caused by outsiders' interference.In the analysis of electromagnetic interference, the system software is the design scheme, management methods and manipulation of electrical equipment or electronic products.
1.1 internal interference
The interference sources inside the system software can be divided into:
(1) switching power supply interference.The key of switching power supply interference is to infiltrate the system software with switching power supply and switching power lead.
(2) ground interference.Ground interference is caused by the use of the same ground wire in the system software. When the current of each part of the power circuit in the system software passes through the public ground wire, the current will be generated on the ground wire and the noise of mutual influence will be generated.
(3) coupling interference of signal safety channel.If signal must be a long transmission line, the signal is very vulnerable to interference in the transmission process, causes the battery change or loss of the frame of transmission signal, the interference caused by the key has a transmission line around the interior space magnetic field of electromagnetic interference of a transmission line: when two root or root around the transmission signal and different signal lines by very close to each other, according to the line between the line of contact resistance and mutual inductance between interference, namely the crosstalk between the line of a transmission line.
1.2 external interference
The external interference sources of the system software can be divided into:
(1) interference of course.Interference, of course, involves the conversion of electrical fields to lightning strikes and air.Lightning strike can cause high frequency surge voltage with high amplitude on the transmission line and cause interference to the system.
(2) electrical engineering interference.As more and more electronic products are connected to the power engineering backbone, some potential interference will occur when the system software.Such interference includes power line interference, rapid transient, surge, operating voltage transition, flash transient and power line impulse current.
(3) dc interference.Both the power supply equipment and the output line cause dc interference. If a section of the signal transmission line is parallel to the power supply system line, such high-frequency interference will be coupled to the signal network and become interference.
(4) frequency interference.Communication equipment, radio broadcasts, television sets, radar detection, etc., send distinct signals based on wireless antennas.
(5) electrostatic discharge.The selection of contemporary integrated IC processing technology, in the small geometric specifications of components have been increasingly gathered, this high speed, millions of triode coordination is very high, very easy to suffer from external electrostatic discharge damage and damage.
(6) low frequency oscillation of car: low frequency oscillation between VHF and uhf during the whole working process of car.
(7) charge and discharge interference.Partial discharge can be divided into positive arc discharge, negative arc discharge and corona discharge.
(8) glow discharge.Glow discharge is vapor charge discharge.
(9) electro-optic charge and discharge.Electro-optic charge and discharge is the metal material mist charge and discharge, ** typical electro-optic charge and discharge is metal material arc welding.
2. Transmission mode of electromagnetic interference
Electromagnetic interference can be divided into two types according to the transmission mode: transmission interference, the key is the interference signals caused by electronic products according to the conductive medium or public power plug caused interference with each other;Radiation source interference is the interference signal caused by electronic products according to the indoor space sent to another electrical Internet or electronic products.From the perspective of the interfered comparator, the interference coupling can be divided into transmission coupling and radiation coupling.
The way to restrain electromagnetic interference
For the three elements of electromagnetic interference, the following three ways to deal with electromagnetic interference problems are clearly proposed:
(1) restrain electromagnetic interference caused by interference source
(1) block
Shielding means selecting shielding body in the middle of two indoor space regions to carry out protection, in order to manipulate the electrostatic field, electromagnetic field and radio wave from one region to another region of magnetic induction and radiation source.
(2) filter
Filtering is the technique of showing transmission poles to signals within a range of frequencies and zeros to signals within a range of frequencies.
(3) grounding device
Ground wire is the implementation of docking ground device, that is, according to a certain regulation, with the necessary metal material electric conductor or transmission line to connect some ground potential difference in the power circuit, or electronic devices, electrical equipment of a position and ground mutual connection.
(4) go line
Different kinds of signals are transmitted by different cables. It is necessary to prevent the signal cable and the driving force cable from laying close to the parallel surface to reduce the electromagnetic interference.
(2) disconnect the transmission mode of interference.
(3) improve the work ability of relatively sensitive machines and equipment against electromagnetic interference (reduce the sensitivity to interference).
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