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14th Reading > Chp 2 > Flashcards

Chp 2 Flashcards

1
Q

EMI duration classifications

A

Transient and continuous

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2
Q

EMI descriptive classifications

A 
Intentional / unintentional
natural 
low frequency / high frequency
magnetic / electric
external / internal
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3
Q

Solution to External EMI

A

Immunity design

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4
Q

RFI vs EMI

A

Radio frequency interference is a subset of EMI

In the freq range of bands: LF, MF, HF, and VHF (band 5-8), 30kHz to 300 MHz

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5
Q

Solution to RFI on telephony

A

Shielded cabling and screening in concerned areas

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6
Q

Types of EMI generated signals

A

Differential mode

Common mode

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7
Q

Common Mode (CM)

A

Same signal on 2 conductors in circuit.

Locks up logic gates

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8
Q

Differential Mode (DM)

A

Equal and opposite signals on conductors.

Corrupts signals

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9
Q

All cables and shields can act like ______ if installed improperly.

A

Antennae

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10
Q

The higher the transmission rate the _____ the effect of interference.

A

higher

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11
Q

Loop antenna

A

Created by cabling and its ground reference

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12
Q

Ground loop issues arise when

A

multiple ground reference planes are used (causing a CM voltage on cable sheathing)

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13
Q

Ground Loop interference is solved by:

A

Use of pathways and cable trays to connect the multiple ground planes and to mitigate radiated signal effects

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14
Q

When designing a cabling system for EMC, consider:

A
  • Availability of structural steel for grounding
  • bonding infrastructure for EFs, ERs, and TRs
  • ac grounding system design
  • use of surge protection
  • use of shielded cable
  • existing CM or DM levels
  • existing or possible sources of EMI
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15
Q

EMI effects are mitigated best at low and high frequencies by

A

Low: cable twists absorb major part

High: cable shield absorbs most

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16
Q

Main factors in unwanted signal coupling

A

1- effectiveness of shield/screen

2- termination implementation

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17
Q

Grounding of cable shields shall

A

be made using a 360 degree connection avoiding breaches in continuity

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18
Q

Typical EMI sources

A

Motors, transformers, lighting, copiers, equipment cords, terminals, power cables

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19
Q

Avoid EMI by

A

maintaining physical separation

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20
Q

EMI should be considered when designing the ______ system

A

pathway

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21
Q

Effect of EMI on fiber optic cables

A

none

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22
Q

Low voltage data lines should not be run in parallel to _________

A

high voltage power lines

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23
Q

Terminate unused conductor at ________ or remove _______

A

both ends, altogether

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24
Q

In critical circuits, use _______

A

optical fiber or well balanced twisted pairs

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25
Q

Device used for mitigating EMI effects

A

isolation transformer

26
Q

Isolation transformers are commonly used in ____ applications and perform the following functions to mitigate EMI:

A

LAN;

  • interrupt the CM ground loop
  • CM rejection and DM signal processing without distortions or other alterations on signal
  • impedance matching
  • balance-to-unbalance conversion
27
Q

Iso transformers reject CM by

A

drains both CM branches to ground via primary coil center tap

28
Q

Mode conversion is

A

when CM voltage is transferred from a transformers primary to secondary resulting in DM noise

29
Q

EMC filtering components:

A

Ferrite toroids, beads, and sleeves

30
Q

When cable sheath grounding is not efficient enough _____ are added to the horizontal cabling system

A

ferrite toroids, beads, and sleeves

31
Q

DM type ferrites are installed ________

A

on each individual conductor

32
Q

CM ferrites are installed ____________

A

around all conductors/cables

33
Q

To mitigate emission problems, ferrites shall be installed on the _______ end

A

source cable

34
Q

To mitigate susceptibility issues, the ferrite shall be installed at the ______ to the susceptible unit

35
Q

(?*)Grounding cable sheaths/shields is not effective enough for signals with _______ frequencies

36
Q

In concept and calculation a well-balanced pair is assumed. In practice, cables and connecting hardware exhibit a ______ in capacitance, resistance, and inductance between conductor and ground.

A

finite unbalance

37
Q

Longitudinal conversion transfer loss in decibels is a measure of the conversion from ________ to _______ because of cabling _________.

A

CM, DM, unbalance

38
Q

A joint-use tunnel is

A

telephone transmission facility place in joint-use with electrical power distribution

39
Q

3 major components of joint-use tunnel problems

A

1- induced EMF from power lines
2- coupling between power and telecom systems
3- the susceptibility of the telecom system

40
Q

In joint-use tunnels, the magnitude of the electrical power-line influence is determined by 2 factors:

A

1- magnitude of current that propagates over the power cable

2- physical config of the line

41
Q

Methods of minimizing power line influence in joint-use tunnel:

A
  • using well balanced three phase systems

- utilizing filters to reduce harmonics

42
Q

Coupling from mutual inductance and mutual capacitance is determined by:

A
  • physical separation distance
  • length of exposure (length in which cables are ran parallel to one another)
  • impedance of the return ground loop
  • shielding effectiveness
43
Q

______ reduce the susceptibility of cabling systems to external fields

A

Cable shields

44
Q

The 2 main effects of induced EMI are due to

A

1- cable acting as an antenna (cable connection to system)

2- conducted interference due to ground-loop effect

45
Q

Worst offenders in terms of unwanted signals are:

A

high-frequency transients generated by starting and stopping machinery

46
Q

Recommended longitudinal balance at low frequencies

A

60dB or greater

47
Q

Recommended longitudinal balance at high frequencies

A

30dB to 40dB or greater

48
Q

*****ADD CARDS FOR PHYSICAL SEP TABLE

49
Q

Unshielded power lines or electrical equipment in proximity to open or non-metal pathways.

A

610mm

24in

50
Q

Unshielded power lines or electrical equipment in proximity to a grounded metal conduit pathway.

A

305mm

12in

51
Q

Power lines enclosed in a grounded metal conduit (or equivalent shielding) in proximity to a grounded metal conduit pathway.

52
Q

Electric motors and transformers

A

1220mm

48in

53
Q

Additional separation precautions must be adhered to when systems are above ________.

54
Q

Separation requirements between metallic cabling and flourescent lamps

55
Q

Separation requirements between metallic cabling and neon lamps

56
Q

Separation requirements between metallic cabling and mercury-vapor lamps

57
Q

Separation requirements between metallic cabling and high-intensity discharge (HID) lamps

58
Q

Separation requirements between metallic cabling and arc welders

A

780mm

31in

59
Q

Separation requirements between metallic cabling and frequency induction heating

A

991mm

39in

60
Q

Where product supplier guarantees do not exist, analysis shall be performed identify ____________

A

EMI sources and possible disturbances

e.g., frequency range, harmonics, transients, bursts, transmitted power

61
Q

Separation requirements specify the _______ distance cabling must be from EMI sources

62
Q

Another term for mode conversion

A

Balance-to-unbalance conversion

14th Reading (13 decks)

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