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49 Cards in this Set
- Front
- Back
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What is Electromagnetic Compatibility?
(2-1) |
The ability of a device, equipment, or system to operate properly in its intended electromagnetic environment without introducing significant EMI into the environment. |
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The coupling between two circuit or system can occur because of one or more of the following mechanisms:
(2-1) |
- Conductive Coupling - Inductive Coupling - Capacitive Coupling - Electromagnetic Coupling |
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Three essential elements to any EMC problem are:
(2-1) |
- Source - Susceptible System or Device - Coupling Path |
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Electromagnetic spectrum includes the following:
(2-2)* |
light, radio waves, microwaves, infrared radiation, ultraviolet rays, x-rays, and gamma rays. |
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Visible light has a frequency of how many hertz?
(2-2) |
10^15 (1Petahertz=1PHz) |
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True or False: Visible light is a large portion of the electromagnetic spectrum.
(2-3) |
False: Visible light represents only a small portion of the electromagnetic spectrum. |
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True or False: Electronic equipment is becoming increasingly sophisticated and the performance levels, operating speeds, and frequencies are rising.
(2-3) |
True |
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Sophisticated electronics use solid state devices that are more susceptible to what kind of interference?
(2-3) |
Electromagnetic Interference (EMI) |
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Conducted coupling may affect electronic devices primarily through the following:
(2-3)* |
- Input signal lines - output signal lines - Utility or premises power distribution |
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Radiated interference enters electronic devices primarily by means of what four sources?
(2-3) |
- Proximity to interfering sources - missing or inadequate gaskets/enclosures - missing or inadequate bonding system components - missing or inadequate device or cable shielding |
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True or False: An ITS systems designer is directly responsible for a the EMC of a ITS.
(2-4) |
False: An ITS systems designer is directly responsible for the EMI of ITS |
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External EMI sources typically include the following:
(2-5) |
- Radio transmitters/Receivers - Electrical power lines - radar - cell phones - engine ignition - lightning - ESD - Electric Motors - Electronic Ballasts |
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Internal EMI sources include the following:
(2-6)* |
- power supplies - power cables - rectifiers - oscillators - digital clocks - digital signal processors - common mode signaling - variations in AC power (sags, swells, UV) - unbalance of AC current - power signaling circuits - power conditioners (UPS) |
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True or False: EMI sources are usually harder to control since it is impossible to reduce emissions at the source.
(2-6) |
False: EMI sources are easier to control since it is possible to reduce emissions at the source. |
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Some examples of causes and effects of EMI include:
(2-7)* |
- Visual distortion on TV signal when the common power source is shared (Vacuum Cleaner) - Audible distortion on AM frequency caused by proximity to a power line. - Physical damage caused by lightning - Visual distortion caused by proximity to strong magnetic fields (ballasts, transformers, ac power circuits) - degradation of circuits exposed to ESD - erasing of files on magnetic media caused by exposure to EM fields - bit parity errors caused by interference from sources on the paths where the information is transferred. |
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These type of monitors are susceptible to RFI from the environment
(2-7)* |
Cathode Ray Tube |
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EMI and RFI are often used interchangeably. RFI is a form of EMI. RFI can be defined as the following:
(2-7) |
the degradation of a desired signal at the receptor end caused by radio frequency disturbance. |
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All EMI problems are explainable by the following:
(2-16) |
The basic laws of physics. The EMI problem is always a circuit. |
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True or False: EMI can be man made or naturally occurring.
(2-18)* |
True |
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Natural sources of EMI include the following:
(2-18) |
- atmospheric electricity (Lightning) - Cosmic radiation or geomagnetism disturbances (solar flares) |
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Man made sources of EMI include the following:
(2-18)* |
- Electrical Power - Communications Electronics - Relay Communications - Tools and Machines - Ignitions Systems - Industrial and Consumer equipment or products |
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Copper cables can ________ unwanted signal or ________ an electromagnetic field when attached to equipment.
(2-20) |
Conduct; radiate |
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Improper shielding, filtering, and grounding can increase the following:
(2-20) |
EMI susceptability |
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There are three types of ESD. They are the following:
(2-21)* |
- Discharge through spark in the air - radiated effect of ESD - contact discharge
(Voltage is typically 2900v to see and hear) |
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The voltage levels for contact type of discharge for level 1, level 2, level 3, and level 4 are:
(2-22)* |
2kV, 4kV, 6kV, 8kV
1 x 2 = 2 2 x 2 = 4 3 x 2 = 6 4 x 2 = 8 |
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The voltage levels for air type of discharge for level 1, level 2, level 3, and level 4 are:
(2-22)* |
2kV, 4kV, 8kV, 15kV |
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Equipment should be verified as properly tested or certified for immunity to radiated fields within what kind of frequency range?
(2-26) |
Wide; a few kilohertz to gigahertz frequencies |
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How are electrical fast transient (EFT) disturbances created?
(2-26) |
when inductive and capacitive circuits are switched on and off over an operation cycle |
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What are two types of unwanted signals on cables in an EMI event?
(2-28) |
Common Mode (CM) and Differential Mode (DM)
CM interferences goes to ground DM interferences is on the phase |
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DM interference mitigation can be accomplished by the following method:
(2-28) |
using individual ferrite beads installed on each input lead of the victim line or output lead of the interfering circuit or line. |
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CM interference can affect the equipment in the following two ways:
(2-28) |
- directly affect equipment operation (locking up) - CM can convert to a DM signal by the cable or equipment |
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Electrical power converters typically produce what kind of unwanted signal?
(2-30) |
Both CM and DM |
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What can help reduce the effects of EMI?
(2-31) |
Proper bonding and grounding |
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These can be a source of EMI in shielded cabling systems where the earth or inadequately bonded grounding references cause a CM voltage to develop between to earth references.
(2-31)* |
Ground loops |
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Important items to consider when designing a cabling system for EMC are:
(2-31) |
- availability of structural steel - bonding infrastructure for EF, ER, and TR - AC grounding electrode system - AC equipment grounding systems - use of surge protection - use of shielded cable - existing CM or DM disturbance levels - existing or possible sources of EMI |
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At low frequencies, cable shields can be grounded at one end. At higher frequencies, cable shields should be grounded at both ends to reduce the effects of EMI. What is the cutoff frequency of low to high?
(2-32) |
1 MHz |
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Metallic conduit is desirable for controlling the effects of what?
(2-36) |
EMI |
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What is the minimum separation distance from EMI sources exceeding 5 kVA, if the source is unshielded power lines or electrical equipment in proximity to open or nonmetal pathways?
(2-44) |
24 inches |
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What is the minimum separation distance from EMI sources exceeding 5 kVA, if the source is unshielded power lines or electrical equipment in proximity to grounded metal pathways?
(2-44) |
12 inches |
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What is the minimum separation distance from EMI sources exceeding 5 kVA, if the source is power lines in metal conduit in proximity to grounded metal pathways?
(2-44) |
6 inches |
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What is the minimum separation distance from EMI sources exceeding 5 kVA, if the source is electric motors and transformers?
(2-44) |
48 inches |
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The minimum cable separation distance from fluorescent lamps, neon lamps, mercury vapor lamps, HID lamps is what?
(2-45) |
5 inches |
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A successful filtering scheme shall provide the following:
(2-47) |
- for the maintenance of signal integrity - effective attenuation of hight frequency unwanted signals as well as broadband CM unwanted signal |
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Ferrite toroids, beads, and sleeves are efficient components used to mitigate EMI and are typically considered this kind of device:
(2-48) |
Filter; chokes are not considered filters |
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The three major components of EM induced interference problem relating to the telephone transmission facilities placed in a joint use utility tunnel with an electrical power systems are:
(2-52) |
- induced EM fields from the power system - coupling between the power and communications systems - susceptibility of the communications system |
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Two characteristics of the telecommunications circuit that determine susceptibility are the:
(2-56) |
- amount or presence of shielding provided by the cable sheath or by the ground conductors - balance of communications circuits |
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The potential difference between two grounds shall be no greater than _______ Vrms to avoid problems with conductive ground loops.
(2-56) |
1.0 |
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What is the recommended overall longitudinal balance at low frequencies (voice)?
(2-56)* |
60 dB |
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What is the recommended overall longitudinal balance at higher frequencies (1-300MHz)?
(2-56)* |
30 to 40 dB |
