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TDMM Chapter 2 Flashcards

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1
Q

EMC

A

Electromagnetic Compatibility
Ability of a device, equipment or system to operate properly in its intended electromagnetic environment without introducing significant electromagnetic interference (EMI) into the environment

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2
Q

EMI

A

Electromagnetic Interference
The transfer of electromagnetic energy from one device or system to another device or system operating in the same environment that causes interference with normal operation of the devices or systems

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3
Q

Electromagnetic Emission

A

The phenomenon by which electromagnetic energy emanates from a source.

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4
Q

Electromagnetic Immunity

A

The ability of a device, equipment or system to perform without degradation in the presence of an electromagnetic disturbance.

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5
Q

EMR

A

Electromagnetic Radiation
Radiation composed of oscillating electrical and magnetic fields and propagated through a medium

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6
Q

ESD

A

Electrostatic Discharge
The sudden flow of electricity between two electrically charged objects caused by contact

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7
Q

Ground Loop

A

Two parallel paths that have identical conductive terminations to two separate grounding (earthing) references

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8
Q

RFI

A

Radio Frequency Interference
The degradation of a desired signal at the receptor end caused by radio frequency disturbance within the radio frequency system.

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9
Q

Two devices are using overlapping operational frequencies within the same EM environment. What is the likely affect on the potential for EMI in this environement?

A

The potential for EMI is likely to increase under these conditions

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10
Q

Name four mechanisms that can create coupling between two circuits or systems

A
  • Conductive coupling
  • Inductive coupling
  • Capacitive coupling
  • Electromagnetic coupling
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11
Q

What type of coupling may occur when a common ac branch circuit is shared between two devices?

A

Conductive Coupling

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12
Q

What causes inductive coupling?

A

Magnetic fields

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13
Q

What causes capacitive coupling?

A

Electric Fields

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14
Q

Name three essential elements of any EMC problem

A
  • Source of an EMI or electromagnetic energy transfer
  • Susceptible device or system that cannot perform as designed because of EMI event
  • Coupling path that promotes the disturbance
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15
Q

Name 8 examples of EMR

A
  • Gamma Rays
  • X Rays
  • UV light
  • Visible light
  • IR Radiation
  • Radar
  • Microwaves
  • Radio Waves
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16
Q

What is the speed of light?

A

300,00kms (186,300 mi/s) in a vacuum

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17
Q

Name the two characteristics that are used to distinguish electromagnetic waves

A
  • wavelength (expressed in meters)
  • Frequency (expressed in hertz)
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18
Q

How many frequency bands are recognized by the ITU?

A

12

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19
Q

True or False
Visible light represents the largest portion of the electromagnetic spectrum

A

False
Visible light represents only a small portion

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20
Q

Name the three primary paths through which conducted coupling may affect electronic devices

A
  • Input signal lines
  • Output signal lines
  • Utility or premises electrical power distribution
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21
Q

Name the four primary conditions that allow radiated interference to enter electronic devices

A
  • Proximity to source
  • Missing gasket/enclosure
  • Missing bonding and grounding system
  • Missing shielding
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22
Q

True or False
Electrical codes do not generally provide for EMC

A

True

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23
Q

What is an electromagnetic field?

A

An area of energy that surrounds electrical devices

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24
Q

What type of charge creates an electric field?

A

Stationary

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25
Normally, it is not practical to control external sources of EMI. What methods should the ICT designer use to address this type of EMI instead?
Revert to methods that promote system immunity
26
What is a reliable and effective technique for mitigating the effects of radio frequency interference on telephone sets?
Deploying shielded or screened structured cabling systems in concerned areas.
27
Why is it difficult to determine a devices EMC?
Because its value is relative to the environment in which it will operate
28
Name the two components of EMC
- Emission - Immunity
29
What units of measure are used to describe magnetic fields?
Amperes per meter
30
What frequency spectrum is typically used for measuring conducted interefernce?
100 kHz to 30 MHz
31
What frequency spectrum is typically used for measuring radiated interference?
30 MHz to 5 GHz
32
How is immunity to radiated emissions determined?
By exposing the device being measured to a specified electromagnetic field and monitoring its performance
33
Name four types of radiated interference measurements
- Anechoic chamber - TEM cell - Reverberating chamber - GHz TEM cell
34
Name three types of conducted interference measurements
- CM and DM interferences - Conducted electromagnetic noise of power supply lines - Conducted EMI from equipment
35
What is the acceptance criteria for field intensity for telecommunications equipment and cabling?
3 V/m maximum
36
What major parameters are likely to fail field testing on a trial link if elevated levels of EMI are present?
Crosstalk (such as NEXT and ANEXT)
37
What design factor could cause EMI on a telecommunications system?
Excessive lengths of unshielded cable between rooms of buildings
38
Name four design factors that could cause EMI on a sites telephone distribution system?
- Unbalanced cabling - Incorrect or missing primary protectors - Incompatible secondary protectors - Incorrect or missing grounds
39
What is the aim of EMC?
To ensure that equipment items or systems will not interfere with or prevent each others operation through spurious emission and absorption of EMI
40
What is the focus of EMC?
To control EMI
41
True of False The EMI problem is always a circuit?
True
42
True or False EMI is often easy to remedy once the root cause is identified
True
43
Name three common sources of EMI problems
- Emission sources - Propagation sources - Receiving or receptor elements
44
Name two natural sources of EMI
- Atmospheric electricity - Cosmic radiation or geomagnetism disturbances
45
Name six man made sources of EMI
- Electrical power - Communications electronics - Relay communications - Tools and machines - Ignition systems - Industrial and consumer equipment or products (non motor)
46
Name three methods used to suppress or prevent unwanted signals
- Shielding - Filtering - Bonding and grounding
47
Name three types of ESD
- Discharge through a spark in the air - Radiated effects of ESD - Contact discharge
48
How many levels of immunity are used to describe ESD?
Four
49
What voltage level is associated with Level 1 immunity for contact discharge?
2 kV
50
What voltage level is associated with Level 2 immunity for contact discharge?
4 Kv
51
What voltage level is associated with Level 3 immunity for contact discharge?
6 kV
52
What voltage level is associated with Level 4 immunity for contact discharge?
8 kV
53
What voltage level is associated with Level 1 immunity for air discharge?
2 kV
54
What voltage level is associated with Level 2 immunity for air discharge?
4 kV
55
What voltage level is associated with Level 3 immunity for air discharge?
8 kV
56
What voltage level is associated with Level 4 immunity for air discharge?
15 kV
57
What is the electrostatic discharge susceptibility voltage range for vertical metal oxide semiconductors?
30 to 1800 V
58
What is the electrostatic discharge susceptibility voltage range for operational amplifiers?
190 to 2500 V
59
What is the electrostatic discharge susceptibility voltage range for resistors?
300 to 3000 V
60
What can cause a telecommunications cable to store energy and then discharge it as ESD?
Mutual capacitance
61
What is the relationship between the category of a balanced cable and its ability to store energy?
The higher the cable category, the lower its ability to store energy
62
What is the mutual capacitance range for category 3 cable?
64 to 66 pF/m
63
What is the mutual capacitance range for category 5e cable?
44 to 49 pF/m
64
What is the mutual capacitance range for category 6 cable?
44 to 46 pF/m
65
What is the mutual capacitance range for category 6A cable?
43 to 45 pF/m
66
What is the mutual capacitance range for category 8 cable?
1.2 pF/m
67
Name the two types of unwanted signals on a cable in an EMI event
- Common Mode (CM) - Differential Mode (DM)
68
Which type of unwanted signal involves a ground plane?
Common Mode (CM)
69
When does a CM signal become evident?
Only when measured against a reference ground
70
How do CM (Common Mode) unwanted signals directly affect equipment operation?
By entering the equipment and causing logical errors
71
What is the primary way that DM (Differential Mode) noise affects equipment?
By corrupting transmitted signals on a balanced circuit
72
What is the relationship between the transmission rate of cabling and interference?
The higher the transmission rate, the higher the effect of the intereference
73
What term describes two parallel paths that have identical conductive terminations to two separate grounding (earthing) references?
Ground Loop
74
True or False The earth is always one of the parallel paths between the grounding references in a ground loop
False The earth is often, but not always on of the paths
75
What is the purpose of electromagnetic shielding?
To reduce or prevent coupling of undesired radiated electromagnetic energy into a system
76
Name the two approaches to using cable shielding as an EMI mitigation technique
- Low frequency noise mitigation - High frequency noise mitigation
77
What absorbs the majority of EMI effects at lower frequencies?
Cable twists
78
What part of the cable absorbs the majority of EMI effects at higher frequencies?
The cable shield
79
How does passing through a medium affect the amplitude of an electromagnetic wave?
It decreases exponentially
80
What parameter best describes the cable shielding response?
Shielding effectiveness
81
What is transfer impedance?
A ratio of the voltage induced on the inside surface of the shield to the current flowing on its outside surface
82
What type of connection is made to ground cable shields?
A 360 degree connection avoiding breaches in the conductor continuity
83
What type of cable has been the traditional choice for buildings with high levels of ambient EMI?
Shielded cable
84
What device may be used in branch circuits to limit the propagation of electrical surges and associated intereference?
Surge protectors
85
How does cable category for balanced twisted pair cable relate to noise?
A higher category results in better noise rejection response
86
What should be used to reduce EMI when signal lines are found close to switchgear?
Localized magnetic barriers
87
Name five methods for reducing EMI from fluorescent lighting
- Shielding grid over lamp - shielded cable between lamp and switch - metal enclosed power switch - filter between power switch and power line - shield electrical cabling
88
Name two means of reducing high levels of noise on power branch circuits
- Line conductors - Surge protectors
89
What is the minimum recommended separation distance between unshielded power lines and non metal telecommunications pathways?
24"
90
What is the minimum recommended distance between an electric motor or transformer and telecommunications pathways?
48"
91
What is the minimum recommended separation distance between metallic cabling and a fluorescent lamp?
5"
92
True of False An electric power line EMI filter is mandatory in all active equipment
True
93
What is the primary function of an isolation transformer for data signals?
To interrupt the CM ground loop at the receiver or transmitter end
94
Define mode conversion
Transfer of CM voltage to a secondary of the transformer as DM noise
95
Where are isolation transformers commonly used?
In LAN and other digital communications applications
96
What is the desirable minimum CMRR for high quality chokes?
40 dB
97
Name two factors that determine the magnitude of electrical powerline influence
- Current that propagates over the power line - Physical configuration of the line
98
Name the two characteristics of telecommunications circuits that determine susceptibility
- Amount of presence of shielding - Balance of the telecommunications circuit
99
What is the recommended overall longitudinal balance for use at low frequencies?
60 dB or greater
100
What is the recommended overall longitudinal balance for use at high frequencies?
30 to 40 dB or greater

DB (19 decks)

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