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DB > TDMM Chapter 2 > Flashcards

TDMM Chapter 2 Flashcards

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
Q

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?

A

Revert to methods that promote system immunity

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26
Q

What is a reliable and effective technique for mitigating the effects of radio frequency interference on telephone sets?

A

Deploying shielded or screened structured cabling systems in concerned areas.

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27
Q

Why is it difficult to determine a devices EMC?

A

Because its value is relative to the environment in which it will operate

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28
Q

Name the two components of EMC

A
  • Emission
  • Immunity
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29
Q

What units of measure are used to describe magnetic fields?

A

Amperes per meter

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30
Q

What frequency spectrum is typically used for measuring conducted interefernce?

A

100 kHz to 30 MHz

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31
Q

What frequency spectrum is typically used for measuring radiated interference?

A

30 MHz to 5 GHz

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32
Q

How is immunity to radiated emissions determined?

A

By exposing the device being measured to a specified electromagnetic field and monitoring its performance

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33
Q

Name four types of radiated interference measurements

A
  • Anechoic chamber
  • TEM cell
  • Reverberating chamber
  • GHz TEM cell
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34
Q

Name three types of conducted interference measurements

A
  • CM and DM interferences
  • Conducted electromagnetic noise of power supply lines
  • Conducted EMI from equipment
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35
Q

What is the acceptance criteria for field intensity for telecommunications equipment and cabling?

A

3 V/m maximum

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36
Q

What major parameters are likely to fail field testing on a trial link if elevated levels of EMI are present?

A

Crosstalk
(such as NEXT and ANEXT)

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37
Q

What design factor could cause EMI on a telecommunications system?

A

Excessive lengths of unshielded cable between rooms of buildings

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38
Q

Name four design factors that could cause EMI on a sites telephone distribution system?

A
  • Unbalanced cabling
  • Incorrect or missing primary protectors
  • Incompatible secondary protectors
  • Incorrect or missing grounds
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39
Q

What is the aim of EMC?

A

To ensure that equipment items or systems will not interfere with or prevent each others operation through spurious emission and absorption of EMI

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40
Q

What is the focus of EMC?

A

To control EMI

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41
Q

True of False
The EMI problem is always a circuit?

A

True

42
Q

True or False
EMI is often easy to remedy once the root cause is identified

A

True

43
Q

Name three common sources of EMI problems

A
  • Emission sources
  • Propagation sources
  • Receiving or receptor elements
44
Q

Name two natural sources of EMI

A
  • Atmospheric electricity
  • Cosmic radiation or geomagnetism disturbances
45
Q

Name six man made sources of EMI

A
  • Electrical power
  • Communications electronics
  • Relay communications
  • Tools and machines
  • Ignition systems
  • Industrial and consumer equipment or products (non motor)
46
Q

Name three methods used to suppress or prevent unwanted signals

A
  • Shielding
  • Filtering
  • Bonding and grounding
47
Q

Name three types of ESD

A
  • Discharge through a spark in the air
  • Radiated effects of ESD
  • Contact discharge
48
Q

How many levels of immunity are used to describe ESD?

A

Four

49
Q

What voltage level is associated with Level 1 immunity for contact discharge?

A

2 kV

50
Q

What voltage level is associated with Level 2 immunity for contact discharge?

A

4 Kv

51
Q

What voltage level is associated with Level 3 immunity for contact discharge?

A

6 kV

52
Q

What voltage level is associated with Level 4 immunity for contact discharge?

A

8 kV

53
Q

What voltage level is associated with Level 1 immunity for air discharge?

A

2 kV

54
Q

What voltage level is associated with Level 2 immunity for air discharge?

A

4 kV

55
Q

What voltage level is associated with Level 3 immunity for air discharge?

A

8 kV

56
Q

What voltage level is associated with Level 4 immunity for air discharge?

A

15 kV

57
Q

What is the electrostatic discharge susceptibility voltage range for vertical metal oxide semiconductors?

A

30 to 1800 V

58
Q

What is the electrostatic discharge susceptibility voltage range for operational amplifiers?

A

190 to 2500 V

59
Q

What is the electrostatic discharge susceptibility voltage range for resistors?

A

300 to 3000 V

60
Q

What can cause a telecommunications cable to store energy and then discharge it as ESD?

A

Mutual capacitance

61
Q

What is the relationship between the category of a balanced cable and its ability to store energy?

A

The higher the cable category, the lower its ability to store energy

62
Q

What is the mutual capacitance range for category 3 cable?

A

64 to 66 pF/m

63
Q

What is the mutual capacitance range for category 5e cable?

A

44 to 49 pF/m

64
Q

What is the mutual capacitance range for category 6 cable?

A

44 to 46 pF/m

65
Q

What is the mutual capacitance range for category 6A cable?

A

43 to 45 pF/m

66
Q

What is the mutual capacitance range for category 8 cable?

A

1.2 pF/m

67
Q

Name the two types of unwanted signals on a cable in an EMI event

A
  • Common Mode (CM)
  • Differential Mode (DM)
68
Q

Which type of unwanted signal involves a ground plane?

A

Common Mode (CM)

69
Q

When does a CM signal become evident?

A

Only when measured against a reference ground

70
Q

How do CM (Common Mode) unwanted signals directly affect equipment operation?

A

By entering the equipment and causing logical errors

71
Q

What is the primary way that DM (Differential Mode) noise affects equipment?

A

By corrupting transmitted signals on a balanced circuit

72
Q

What is the relationship between the transmission rate of cabling and interference?

A

The higher the transmission rate, the higher the effect of the intereference

73
Q

What term describes two parallel paths that have identical conductive terminations to two separate grounding (earthing) references?

A

Ground Loop

74
Q

True or False
The earth is always one of the parallel paths between the grounding references in a ground loop

A

False
The earth is often, but not always on of the paths

75
Q

What is the purpose of electromagnetic shielding?

A

To reduce or prevent coupling of undesired radiated electromagnetic energy into a system

76
Q

Name the two approaches to using cable shielding as an EMI mitigation technique

A
  • Low frequency noise mitigation
  • High frequency noise mitigation
77
Q

What absorbs the majority of EMI effects at lower frequencies?

A

Cable twists

78
Q

What part of the cable absorbs the majority of EMI effects at higher frequencies?

A

The cable shield

79
Q

How does passing through a medium affect the amplitude of an electromagnetic wave?

A

It decreases exponentially

80
Q

What parameter best describes the cable shielding response?

A

Shielding effectiveness

81
Q

What is transfer impedance?

A

A ratio of the voltage induced on the inside surface of the shield to the current flowing on its outside surface

82
Q

What type of connection is made to ground cable shields?

A

A 360 degree connection avoiding breaches in the conductor continuity

83
Q

What type of cable has been the traditional choice for buildings with high levels of ambient EMI?

A

Shielded cable

84
Q

What device may be used in branch circuits to limit the propagation of electrical surges and associated intereference?

A

Surge protectors

85
Q

How does cable category for balanced twisted pair cable relate to noise?

A

A higher category results in better noise rejection response

86
Q

What should be used to reduce EMI when signal lines are found close to switchgear?

A

Localized magnetic barriers

87
Q

Name five methods for reducing EMI from fluorescent lighting

A
  • 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
Q

Name two means of reducing high levels of noise on power branch circuits

A
  • Line conductors
  • Surge protectors
89
Q

What is the minimum recommended separation distance between unshielded power lines and non metal telecommunications pathways?

A

24”

90
Q

What is the minimum recommended distance between an electric motor or transformer and telecommunications pathways?

A

48”

91
Q

What is the minimum recommended separation distance between metallic cabling and a fluorescent lamp?

A

5”

92
Q

True of False
An electric power line EMI filter is mandatory in all active equipment

A

True

93
Q

What is the primary function of an isolation transformer for data signals?

A

To interrupt the CM ground loop at the receiver or transmitter end

94
Q

Define mode conversion

A

Transfer of CM voltage to a secondary of the transformer as DM noise

95
Q

Where are isolation transformers commonly used?

A

In LAN and other digital communications applications

96
Q

What is the desirable minimum CMRR for high quality chokes?

A

40 dB

97
Q

Name two factors that determine the magnitude of electrical powerline influence

A
  • Current that propagates over the power line
  • Physical configuration of the line
98
Q

Name the two characteristics of telecommunications circuits that determine susceptibility

A
  • Amount of presence of shielding
  • Balance of the telecommunications circuit
99
Q

What is the recommended overall longitudinal balance for use at low frequencies?

A

60 dB or greater

100
Q

What is the recommended overall longitudinal balance for use at high frequencies?

A

30 to 40 dB or greater

DB (19 decks)

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