Chapter i
Pdbw = 10lgp, udbv = 20lgu, idba = 20lgi
Chapter ii
What are the three elements of electromagnetic interference? Response: sources of harassment, coupling routes, sensitive units
3. What are the common sources of electromagnetic harassment? How
Answer: (1) from source: natural and artificial harassment
(2) delineation from harassment attributes: functional and non-functional sexual harassment
(3) distinction from a combination: conductive and radiological harassment
(4) from spectrum width: wide and narrow frequency harassment
(5) from frequency range: very low frequency harassment, work and audio harassment, load harassment, radio and video harassment, microwave harassment
6. What are the main ways in which electromagnetic harassment can spread? Response: convergence, magnetic field, electric field, radiation. - yeah
7. Why do you attach particular importance to the path to the return of electricity
(1) any current must be returned to its source, and if we can provide him with a route for high frequency currents, he may (mainly) follow that route, and if such a route is not provided, he will find his own route (not under control)。
(2) the current always follows the least resistance route come on
12. What are the routes that influence magnetic field coupling? How can its impact be reduced
Answer: (1)-jwbscosium, resistance from sources and loads in jamming circuits, syndromic density of sines, angle frequency, area of closed circuits, magnetic flux density and angles on the back road
(2) reduce the frequency of harassing electrical currents, reduce the perception between circuits and reduce the load resistance to interference with circuits
What are the factors affecting the coupling of electric fields? How can its impact be reduced
Answer: (1) the frequency of harassment of the source, harassment of the voltage, harassment of the circuits, coupling of the capacitors, obstruction of the circuit by the source and the load resistance。
(2) reduction of harassment voltage, reduction of the frequency of harassment voltage, reduction of the combination of interference with resistance and load resistance in circuits, reduction of coupling between circuits, appropriate increase of distance between circuits and use of shielding measures。
Chapter iii
The shield can be divided into electric shield, magnetic shield, electromagnetic field shield, and woven belt shield。
1. What is the rationale for electrostatic shielding
When the conductor is placed in the electrostatic field and reaches the electrostatic balance, the conductor is an equation, the internal electric field is zero, there is no static charge in the conductor, and the charge can be distributed only on the surface of the conductor. If there is a cavity inside the conductor and there is no field in the cavity, the cavity conductor acts as a barrier to the external static field. If the body is placed inside an empty cavity, an equivalent charge is detected on the surface of the cavity. If the cavity conductor is connected to the ground, the field will not be generated outside the conductor。
2. What is the rationale for magnetic shielding
The use of high-conducted magnetic materials for magnetic field shielding is the use of its low-obstructive properties to divide the harassing magnetic field and significantly reduce the magnetic field surrounding the area. The magnetic field shield is achieved using conductive materials to generate reverse magnetic fields to offset external magnetic fields. A conductor shield creates a sensor vortex on the surface of the shield under the action of an external high frequency magnetic field, which produces a reverse magnetic field to offset the external magnetic field that passes through the shield。
What is the principle of electromagnetic shielding
Response: the use of shielding prevents electromagnetic waves from spreading in space, and electromagnetic waves produce reflection and absorption while crossing the shield, leading to a weakening of electromagnetic energy。
Chapter iv
What are the main technical indicators for filters
Response: insert loss, frequency characteristics, resistance characteristics, rated voltage, rated currents, outer dimensions, working environment, reliability, etc
2. What does the insertion loss mean? Response: insert loss as il = 20 lg (u1/u2)
4. What are the basic circuits for reflectors
Response: estimation type (l), capacitive type (c), steaming type, resilient type, t-type, b-type, etc。
7. What are the special features of electromagnetic interference filters compared to general filters
Answer: (1) emi filters work against mismatches and must consider their mismatch characteristics in order to ensure better filtering throughout the frequency range。
(2) emi filters are used to suppress electromagnetic harassment, and the characteristics of the source of the harassment must be understood so that it can be used correctly and, if not properly handled, may result in oscillation, malformations, etc。
(3) emi filters are primarily used to suppress high-frequency electromagnetic or transient harassment and use of electrons, parasitic parameters of the electro-capacitating element has a greater impact and must be strictly controlled。
(4) when emi filters are used on power lines, their sensory capacitor elements will be subject to greater voltage and currents, must be assured of sufficient resistance and capacity, and need to prevent the emergence and saturation of the electrons。
What is the role of the power line filter? What parameters should be considered? What are the concerns about use
Response: effect: restraining equipment from conductive launch or increasing resistance to harassment in the grid。
Consider parameters: matching of resistance from sources and load resistance, speciality of power lines。
Note: threading l values in filters cannot be too large, adjoining and conjunctive values cannot be too large, and compost loops can be used in power line filters。
12. What should be taken into account for the installation of filters
Answer: (1) location of installation of filters, (2) segregation of filter input and output fuses。
13. What will be the impact of the parasitic parameters of the component on the filter effect
Answer: (1) non-ideal characteristics of the component: when the frequency of the signal exceeds their frequency of vibration, its real and desired characteristics are very different。
(2) interception: the effect of high-frequency filtering is lower than envisaged when associated with the wave capacity。
(3) emission of the capacitor circuit: the charge release of the capacitors is limited by the receipt of the sensor。
Why is the four end capacitors more suitable for filtering than the two end capacitors?
Response: both end capacitors, in order to reduce the sense of mutuality, can reduce the magnetic coupling of circuits on both sides, e. G., by reducing the length of the capacitors, changing the circuit lines, introducing four-wire capacitors, introducing surfaces。
15. Why is a heart-trapped convulsion an ideal interference filter
A: owing to the special nature of the convulsive convulsion structure, it has a very small wiring sense. The kernel is usually installed on the equipment's conductor shell, which is connected to the ground's equipment shell at 360° and has a near-zero sense of cross-sectional circuits, thus significantly increasing the filtering effect。
Chapter v
What's the location? Why
Response: concept: the equipment or system is linked to the earth (an ideal zero bit face/body)。
Purpose: (1) to avoid direct exposure to the outer shell or to the leaking time shell with electrical charge at high pressure, causing electrocution to the human body that touches the shell。
(2) to provide a public zero-pilot on all unit circuits throughout the circuit system to ensure that the circuit system is stable。
(3) in order to achieve the shielding of the electric field, a sound conductor is required to be used as an electrostatic shield and the shield must be connected to the ground, otherwise the shield will not function as an electrostatic shield, but rather will increase the distribution of the electrical capacitor, thereby strengthening the configuration。
What are the three places? What's its content
Response: (1) safe location: safe location of equipment, safe location of mine
(2) interference control site: floating, single, multiple, mixed
(3) grounding of shielding: low-frequency signal shielding, high-frequency signal shielding
4. What is single-point, multi-point? How
Answer: (1) single point: there is only one reference point in the equipment or circuit unit. Multi-point: each of the interfaces in the equipment or circuit unit is directly connected to the nearest ground level, making the line shortest。
(2) in general, a single-point approach may be used when the frequency is less than 1 mhz or the length of the surface line is less than λ20. When the frequency is higher than 10 mhz, a multi-point approach should be used. For frequencies ranging from 1 to 10 mhz, a single-point approach may be applied if the length of the line is less than λ20, or a multi-point approach。
5. Why is it sometimes connected to the electrical capacity in the equipment
Response: capacitors are equivalent to short circuits for hf and low frequency are equivalent to open circuits。
7. How should the shielding layer of the shielding cable determine how and where to proceed
Response: hf signal shielding shall be multi-pointed and will be used as a multi-point surface for the outer catheter of the axle cable shield, while the distance between adjacent shielding points is generally less than λ20. When the cable is of shorter length, the cable shield is connected to the signal end and the receiving end, respectively。
What's a connection? Try to identify a few ways。
Answer: (1) connect: a point that will require a level connection will be structurally connected by mechanical, chemical and physical means to achieve low resistance。
(2) common methods: welding, tethering, embolism
Chapter vi
2. When electrically sensory loads are broken by mechanical switches, can electrical arcs and electromagnetic harassment occur at the switch's contact point, which is serious when the switch is closed or broken? What measures should be taken to curb harassment
Answer: (1) serious when disconnected (2) 1 resilient at both ends of the load and connect to the diode 2 and collapsively into the resistance 3 at both ends of the load and connected to the condensation 4 at both ends of the load and connected to the condensation 5 with a condensed condensation 6 at both ends of the load and condensed to the sensitivity barrier 7 at both ends of the contact point 8 at both ends of the condensation path 8 and at both ends of the condensed trough and connected to the constriction 9 at both ends pipe
4. What are the commonly used wave inhibitors? What are the characteristics of each and for what occasion
Answer: (1) ejects of electric fire: there are two or three electrodes that can be used for inter-linee or interlineal and inter-surface wave protection。
(2) pressure-sensitive electrical resistance to metal oxide: the peak current tolerance for pressure-sensitive electrical resistance is high and low. More suitable for the work frequency system。
(3) silicon instantaneously absorbs diodes: has a very rapid response time and a fairly high wave absorption capacity and low plier voltage. The range applied to hf and vhf can be used to protect circuits or equipment from electrostatic, switch-to-switch, and lightning-inflicted voltage。
Chapter vii
What are the main electromagnetic compatibility standards
Response: iec of the international electrotechnical commission, cispr of the international special committee on radio interference, electromagnetic compatibility committee tc-77
How many levels does the 2 emf standard system include? What is the general content
Answer: (1) basic standards: other emc standards are designated as the basis, generally not product-specific。
(2) common standard: a minimum requirement for electromagnetic compatibility of a set of standardized test methods and requirements (limit values) for all products in a generic environment。
(3) product standard category: tests for electromagnetic compatibility for certain products。
3. What are the main elements of the electromagnetic compatibility test
Response: hf electromagnetic harassment (emp), low-frequency emp (lhf), product resistance test
4. What does “ccc” certification mean? What are the requirements for electromagnetic compatibility
Answer: (1) china has compulsory authentication (2) of equipment for domestic and similar purposes, electrical tools, audio-visual equipment, information technology equipment, lighting appliances for electromagnetic compatibility testing。
5. What are the main instruments for electromagnetic compatibility measurements
Response: emi receivers, circuits resistant to stabilization networks, antennas, current probes, voltage detectors, 10pf piercings, measuring sites
8. What is the role of circuit resistance to stabilization networks
Answer: (1) provide approximately constant high-pressure resistance to the power source end of the measured equipment to ensure comparability of the different measurements。
(2) separating other interference signals on the electrical network from the interference voltage generated by the detection equipment to ensure the accuracy of the measurements。
(3) provide safe isolation of the measuring end and detected power circuits in order to avoid damage to the input circuits of the electromagnetic interference measurement receivers of the power circuits。
