Chapter 2 Flashcards
EMC
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.
TDMM.* Page 2-1
EMI
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.
TDMM.* Page 2-1
Electromagnetic
Emission
The phenomenon by which
electromagnetic energy
emanates from a source.
Emissions can be either radiated
or conducted when coupled into
a given disturbed circuit. Such
emissions may be divided into
two categories: intentionally
emitted signals and
unintentional emissions.
TDMM.* Page G-67
Electromagnetic
Immunity
The ability of a device,
equipment, or system to perform
without degradation in the
presence of an electromagnetic
disturbance.
TDMM.* Page G-67
EMR
Electromagnetic Radiation
Radiation composed of
oscillating electrical and
magnetic fields and propagated
through a medium.
TDMM.* Page 2-2
ESD
Electrostatic Discharge
The sudden flow of electricity
between two electrically charged
objects caused by contact.
TDMM.* Page 2-79
Ground Loop
Two parallel paths that have
identical conductive
terminations to two separate
grounding (earthing) references.
TDMM.* Page 2-27
RFI
Radio Frequency Interference
The degradation of a desired
signal at the receptor end
caused by radio frequency
disturbance within the radio
frequency system which is
usually comprised in the
frequency range that includes
LF, MF, I-IF, and VHF.
TDMM.* Page 2-8
Two devices are using
overlapping operational
frequencies within the
same EM environment.
What is the likely affect on
the potential for EMI in this
environment?
The potential for EMI is likely to
increase under these conditions.
TDMM.* Page 2-1
Name 4 mechanisms that can create coupling between two circuits or systems.
- Conductive coupling
- Inductive coupling
- Capacitive coupling
- Electromagnetic coupling
TDMM: Page 2-1
What type of coupling may
occur when a common ac
branch circuit is shared
between two devices?
Conductive coupling
TDMM: Page 2-1
What causes
inductive coupling?
Magnetic fields
TDMM.* Page 2-1
What causes
capacitive coupling?
Electric fields
TDMM.* Page 2-1
Name 3 essential elements
of any EMC problem.
- Source of an EMI or
electromagnetic energy transfer - Susceptible device or system
that cannot perform as designed,
configured, or programmed
because of the EMI event - Coupling path that promotes the
disturbance
TDMM.* Page 2-1
Name 8 examples of EMR.
- Gamma rays
- X-rays
- UV light
- Visible light
- IR radiation
- Radar
- Microwaves
- Radio waves
TDMM.* Page 2-2
What is the speed of light?
300,000 km/s (186,300 mi/s) in a vacuum
TDMM.* Page 2-2
Name the 2 characteristics that are used to distinguish electromagnetic waves.
- Wavelength (expressed in meters)
- Frequency (expressed in hertz)
TDMM.* Page 2-2
How many frequency
bands are recognized by
the ITU?
12
TDMM.* Page 2-2
True or False
Visible light represents the
largest portion of the
electromagnetic spectrum.
False. Visible light represents
only a small portion of the
electromagnetic spectrum.
TDMM.* Page 2-3
Name the 3 primary paths
through which conducted
coupling may affect
electronic devices.
1.lnput signal lines
2.0utput signal lines
3.Utility or premises electrical
power distribution
TDMM.* Page 2-4
Name the 4 primary
conditions that allow
radiated interference to
enter electronic devices.
1 .Proximity to interfering sources
2.Missing or inadequate
gaskets/enclosures
3.Missing or inadequate bonding
and grounding (earthing) system
components
4.Missing or inadequate device or
cable shielding
TDMM.* Page 2-4
True or False
Electrical codes do not
generally provide for EMC.
True. Electrical codes do not
generally provide for EMC.
TDMM.* Page 2-4
What is an
electromagnetic field?
An area of energy that surrounds
electrical devices
TDMM.* Page 2-6
What type of charge
creates an electric field?
Stationary
TDMM.* Page 2-6
What type of charge
creates a magnetic field?
Moving
(electrical currents)
TDMM.* Page 2-6
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.
TDMM.* Page 2-6
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
TDMM: Page 2-8
Why is it difficult to
determine a device’s EMC?
Because its value is relative
to the environment in
which it will operate
TDMM.* Page 2-9
Name the 2
components of EMC.
1 .Emission
2.Immunity
TDMM.* Page 2-9
What units of measure
are used to describe
magnetic fields?
Amperes per meter
TDMM.* Page 2-9
What frequency spectrum
is typically used for
measuring conducted
100 kHz to 30 MHz
TDMM.* Page 2-9
What frequency spectrum
is typically used for
measuring radiated
interference?
30 MHz to 5 GHz
TDMM.* Page 2-9
How is immunity to
radiated emissions
By exposing the device being
measured to a specified
electromagnetic field and
monitoring its performance
TDMM.* Page 2-9
Name 4 types of
radiated interference
measurements.
1 .Anechoic chamber
2.TEM cell
3.Reverberating chamber
4.GHz TEM cell
TDMM.* Page 2-70
Name 3 types of
conducted interference
measurements.
1 .CM and DM interferences
2.Conducted electromagnetic
noise on power supply lines
3.Conducted EMI from
equipment
TDMM.* Page 2-10
What is the acceptance
criteria for field intensity for
telecommunications
equipment and cabling?
3 V/m maximum
TDMM.* Page 2-17
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)
TDMM.* Page 2-11
What design factor could cause
EMI on a telecommunications
system?
Excessive lengths of unshielded
cable between rooms
of buildings
TDMM.* Page 2-12, Table 2.1
What 4 design factors could cause EMI on a site’s telephone distribution system?
- Unbalanced cabling
- Incorrect or missing primary protectors
- IncompatibIe secondary protectors
- Incorrect or missing grounds
TDMM.* Page 2-14, Table 2.2
What is the aim of EMC?
To ensure that equipment items
or systems will not interfere with
or prevent each other’s
operation through spurious
emission and absorption of EMI
TDMM.* Page 2-15
What is the focus of EMC?
To control EMI
TDMM.* Page 2-75
True or False
The EMI problem is
always a circuit.
True. The EMI problem
is always a circuit.
TDMM.* Page 2-75
True or False
EMI is often easy to remedy
once the root cause
is identified.
True. EMI is often easy to
remedy once the root cause
is identified.
TDMM.* Page 2-75
Name 3 common sources
of EMI problems.
1 .Conducted and radiated
emission sources
2. Transfer of propagation
sources
3.Receiving or receptor
TDMM.* Pages 2-15 to 2-16
Name 2 natural
sources of EMI.
1 .Atmospheric electricity
2.Cosmic radiation or
geomagnetism disturbances
TDMM.* Page 2-16
Name 6 man-made
sources of EMI.
1.Electrical power
2.Communications electronics
3.Relay communications
4.Tools and machines
5.Ignition systems
6.Industrial and consumer equipment
or products (non-motor/engines)
TDMM.* Pages 2-16 to 2-17
Name 3 methods used to
suppress or prevent
unwanted signals.
- Shielding
- Filtering
- Bonding and grounding
(earthing) of cable shields and
equipment
TDMM.* Page 2-18
Name 3 types of ESD.
1 .Discharge through a spark in
the air
2.Radiated effects of ESD
3.Contact discharge
TDMM.* Page 2-19
How many levels of
immunity are used to
describe ESD?
4
TDMM.* Page 2-19
What voltage level is associated with Level 1 immunity for contact
discharge?
2kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 2
immunity for contact
discharge?
4 kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 3
immunity for contact
discharge?
6 kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 4
immunity for contact
discharge?
8 kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 1
immunity for air discharge?
2 kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 2
immunity for air discharge?
4 kV
TDMM.* Page 2-19, Table 2.3
What voltage level is
associated with Level 3
immunity for air discharge?
8 kV
TDMM: Page 2-19, Table 2.3
What voltage level is
associated with Level 4
immunity for air discharge?
15kV
TDMM.* Page 2-19, Table 2.3
What is the electrostatic
discharge susceptibility
voltage range for vertical
metal oxide
semiconductors?
30 to 1800 v
TDMM.* Page 2-20, Table 2.4
What is the electrostatic
discharge susceptibility
voltage range for
operational amplifiers?
190 to 2500V
TDMM.* Page 2-20, Table 2.4
What is the electrostatic
discharge susceptibility
voltage range for resistors?
300 to 3000 V
TDMM.* Page 2-20, Table 2.4
What can cause a
telecommunications cable
to store energy and then
discharge it as ESD?
Mutual capacitance
TDMM.* Page 2-20
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.
TDMM.* Page 2-21
What is the mutual
capacitance range for
category 3 cable?
64 to 66 pF/m
TDMM: Page 2-27, Table 2.5
What is the mutual
capacitance range for
category 5e cable?
44 to 49 pF/m
TDMM.* Page 2-21, Table 2.5
What is the mutual
capacitance range for
category 6 cable?
44 to 46 pF/m
TDMM: Page 2-27, Table 2.5
What is the mutual
capacitance range for
category 6A cable?
43 to 45 pF/m
TDMM.* Page 2-21, Table 2.5
What is the mutual
capacitance value for
category 8 cable?
1.2 pF/m
TDMM.* Page 2-21, Table 2.5
Name the 2 types of
unwanted signals on a
cable in an EMI event.
1 .Common mode (CM)
2.Differential mode (DM)
TDMM.* Page 2-24
Which type of unwanted
signal involves a
ground plane?
Common mode (CM)
TDMM.* Page 2-24
When does a CM signal
become evident?
Only when measured against a
reference ground
TDMM.* Page 2-24
How do CM unwanted
signals directly affect
equipment operation?
By entering the equipment and
causing logical errors
TDMM.* Page 2-24
What is the primary way
that DM noise
affects equipment?
By corrupting transmitted
signals on a balanced circuit
TDMM.* Page 2-25
What is the relationship
between the transmission
rate of cabling and
interference?
The higher the transmission
rate, the higher the effect of the
interference.
TDMM.* Page 2-26
What term describes two
parallel paths that have
identical conductive
terminations to two
separate grounding
(earthing) references?
Ground loop
TDMM.* Page 2-27
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, one of the parallel paths
between the grounding
references in a ground loop.
TDMM.* Page 2-27
What is the purpose of
electromagnetic shielding?
To reduce or prevent coupling of
undesired radiated
electromagnetic energy into a
given system to enable it to
operate properly in its
electromagnetic environment
TDMM.* Page 2-33
Name the 2 approaches to
using cable shielding as an
EMI mitigation technique.
1 .Low-frequency noise mitigation
2.High-frequency noise mitigation
TDMM.* Page 2-33
What absorbs the majority
of EMI effects at lower
frequencies?
Cable twists
TDMM.* Page 2-33
What part of the cable
absorbs the majority of
EMI effects at higher
frequencies?
The cable shield
TDMM.* Page 2-33
How does passing through
a medium affect the
amplitude of an
electromagnetic wave?
It decreases exponentially.
TDMM.* Page 2-33
What parameter best
describes the cable
shielding response?
Shielding effectiveness
TDMM.* Page 2-33
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
TDMM.* Page 2-34
What type of connection is
made to ground cable
shields?
A 360-degree connection,
avoiding breaches in the
conductor continuity
TDMM.* Page 2-34
What type of cable has
been the traditional choice
for buildings with high
levels of ambient EMI?
Shielded cable
TDMM.* Page 2-35
What device may be used
in branch circuits to limit
the propagation of
electrical surges and
associated interference?
Surge protectors
TDMM.* Page 2-35
How does cable category
for balanced twisted-pair
cable relate to noise?
A higher category results in a
better noise rejection response.
TDMM.* Page 2-36
What should be used to
reduce EMI when signal
lines are found close to
switchgear?
Localized magnetic barriers
TDMM.* Page 2-36
Name 5 methods for
reducing EMI from
fluorescent lighting.
1 .Place a shielding grid over the lamp.
2.Install shielded cable between the lamp
and the electrical power switch.
3.Install a metal-enclosed electrical power
switch.
4. place a filter between the electrical
power switch and the electrical power
line.
5.Shield the electrical power line cable.
TDMM.* Page 2-37
Name 2 means of reducing
high levels of noise on
power branch circuits.
1 .Line conditioners
2.Surge protectors
TDMM.* Page 2-37
What is the minimum
recommended separation
distance between
unshielded power lines and
non-metal
telecommunications
pathways?
=610 mm (24 in)
TDMM: Page 2-38, Table 2.6
What is the minimum
recommended separation
distance between an
electric motor or
transformer and
telecommunications
equipment?
~1220 mm (48 in)
TDMM: Page 2-38, Table 2.6
What is the recommended
minimum separation
distance between metallic
cabling and a fluorescent
lamp?
=127 mm (5 in)
TDMM.* Page 2-38, Table 2.7
True or False
An electric power line EMI
filter is mandatory in all
active equipment.
True. An electric power line EMI
filter is mandatory in all modern
electronics (active equipment)
for conducted emissions or
susceptibility aspects or both.
TDMM.* Page 2-39
What is the primary
function of an isolation
transformer for data
signals?
To interrupt the CM ground loop
at the receiver or transmitter end
TDMM.* Page 2-40
Define mode conversion.
Transfer of CM voltage to a
secondary of the transformer as
DM noise
TDMM.* Page 2-40
Where are isolation
transformers commonly
used?
In LAN and other digital
communications applications
TDMM.* Page 2-40
Where are isolation
transformers commonly
used?
In LAN and other digital
communications applications
TDMM.* Page 2-40
What is the desirable
minimum CMRR for high
quality chokes?
40 dB
TDMM.* Page 2-42
Name 2 factors that
determine the magnitude of
electrical powerline
influence.
1 .Current that propagates over
the power line
2.Physical configuration of the
line
TDMM.* Page 2-44
Name 2 characteristics of
telecommunications
circuits that determine
susceptibility.
- Amount or presence of
shielding - Balance of the
telecommunications circuit
TDMM.* Page 2-47
What is the recommended
overall longitudinal balance
for use at low frequencies?
60 dB or greater
TDMM.* Page 2-48
