Transcript Computer Maintenance

Computer Maintenance
Basic Electricity/Electronics
Copyright © Texas Education Agency, 2011. All rights reserved.
1
Summary Slide
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Parts of an Atom
Types of Electrical Materials
Measuring Electricity
Using a Multimeter to Make Resistance Measurements
Using a Multimeter to Make Voltage Measurements
Signals and Noise in Communication Systems
Measuring Analog Signals
Digital and Analog Signaling
Simplex, Half-Duplex, and Full Duplex Transmission
Baseband and Broadband
Signaling and Communications Problems
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Computer Maintenance: Electronics/BasicElectricity
2
Parts of an Atom
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nucleus - the center part of the atom, formed by
neutrons and protons
protons - particles have a positive charge, and
along with
neutrons,
form the nucleus
neutrons – particles
have no charge
(neutral), and along
with protons, form
the nucleus
electrons - particles have a negative charge, and
orbit the nucleus
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Types of Electrical
Materials
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Insulators - high resistance to electrical
current
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Conductors - conducts the flow of electrons
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plastic, glass, air, wood, paper, rubber
Copper, silver, gold
Semiconductors - control the flow of
electrons
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carbon, silicon
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Measuring Electricity
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Voltage (V) - electrical force or pressure
that occurs when electrons and protons are
separated
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The force that is created pushes toward the
opposite charge and away from the like
charge.
Voltage can also be created by friction (static
electricity), by magnetism (electric generator),
or by light (solar cell).
unit of measurement is VOLT
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Measuring Electricity
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Current (I)—the measurement of electron
flow in an electrical circuit
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unit of measurement is AMPERE (amp)
Resistance (R)—amount of opposition to
current
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unit of measurement is the OHM ()
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Measuring Electricity
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Measuring Electricity
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Electricity is brought to your home, school and
office by power lines.
The power lines carry electricity in the form of
alternating current (AC).
Another type of current called direct current (DC),
can be found in flashlight batteries, car batteries,
and as power for the microchips on the
motherboard of a computer.
It is important to understand the difference
between these two types of current.
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Measuring Electricity
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Alternating Current (AC)
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Direct current (DC)
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Flows in two directions
Flows in one direction only
Impedance (Z) – measured in ohms (Ω)
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Total opposition to current flow (due to AC and
DC voltages)
Resistance – generally used when referring to
DC voltages.
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Measuring Electricity
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Current flows through closed loops called
circuits.
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These circuits must be composed of conducting
materials and have sources of voltage.
The three required parts of an electrical circuit are
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Source or battery
Complete path
Load or resistance
Voltage causes current to flow while resistance and
impedance oppose it.
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Measuring Electricity
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Measuring Electricity
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For AC and DC electrical systems, the flow of
electrons is always from a negatively charged
source to a positively charged source.
For the controlled flow of electrons to occur, a
complete circuit is required.
Electrical current generally follows the path of
least resistance.
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Measuring Electricity
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Because metals such as copper provide little
resistance, they frequently are used as conductors for
electrical current.
Materials such as glass, rubber, and plastic provide
more resistance; they are not good conductors and are
generally used as insulators.
The purpose of connecting the safety ground to
exposed metal parts of computing equipment is to
prevent such metal parts from becoming energized
with a hazardous voltage from a wiring fault inside the
device.
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Using a Multimeter to
Make Resistance
Measurements
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A multimeter can be used to measure:
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Voltage
Resistance
Continuity
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Using a Multimeter to
Make Resistance
Measurements
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If you intentionally make a path into a lowresistance path for use by two connected
electrical devices, then the path has continuity.
If a path is made unintentionally into a lowresistance path, then it is called a short circuit.
The unit of measurement for both is the OHM
(Ω).
Continuity refers to the level of resistance of a
path.
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Using a Multimeter to
Make Resistance
Measurements
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You can perform measurements on the
following:
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CAT 5 cable
Terminated CAT 5 cable
Terminated coaxial cable
Telephone wire
CAT 5 jacks
Switches
Wall outlets
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Using a Multimeter to
Make Voltage
Measurements
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Two types of voltage measurement exist:
DC and AC.
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The meter must be set to DC when
measuring DC voltages. This includes the
following:
Batteries
 Outputs of computer power supplies
 Solar cells
 DC generators
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Using a Multimeter to
Make Voltage
Measurements
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Two types of voltage measurement exist:
DC and AC.
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The meter must be set to AC when
measuring AC voltages.
If you measure a wall socket, you must assume
that line voltage is present.
 Line voltage is 120 V AC in the US and 220 V
AC in most other places around the world
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Signals and Noise in
Communication Systems
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The term signal refers to a desired electrical
voltage, light pattern, or modulated
electromagnetic wave.
Signals can be created as:
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Electrical pulses that travel over copper wire.
Pulses of light that travel through strands of glass or
plastic.
Radio transmissions that travel over the airwaves.
As laser or satellite transmissions.
As infrared pulse.
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Signals and Noise in
Communication Systems
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Two main types of signaling (Analog and
Digital).
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Analog
Change gradually and continuously (will have a
continuously varying voltage – versus – time
graph).
 Typical of things in nature
 Used widely in telecommunications for more than
100 years
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Signals and Noise in
Communication Systems
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Two main types of signaling (Analog and
Digital). (Continued)
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Digital
Change one state to another almost
instantaneously, without stopping at an in-between
state.
 Discrete or jumpy
 Typical of technology instead of nature
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Measuring Analog
Signals
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Analog signals are measured in cycles,
with one cycle representing the change
from high to low and back again.
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Three characteristics are measured:
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Amplitude
Frequency
phase
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Digital and Analog
Signaling
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Digital signaling is the most appropriate format
for transmitting computer data, and most
networks use digital signaling methods for that
reason.
Because it is a simpler technology, digital
signaling has some advantages over analog:
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Generally less expensive to make digital equipment
Generally less vulnerable to errors caused by
interference because the discrete state of on and off is
not as easily affected by a small distortion as is a
continuous wave form.
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Digital and Analog
Signaling
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Analog signals also have advantages:
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Signals can be easily multiplexed; that is signals can be
combined to increase bandwidth.
Signals are less vulnerable to the problem of
attenuation (signal loss due to surroundings), because
of distance so they can travel farther without becoming
too weak for reliable transmission.
 However, when an analog signal is amplified, the noise
is amplified with the signal.
Digital connectivity solutions generally offer better
security, faster performance, and higher reliability.
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Simplex, Half-Duplex,
and Full Duplex
Transmission
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Simplex Transmission
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Half-Duplex Transmission
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Unidirectional – signal travels in only one
direction.
Television is an example.
Signal can travel in both directions but not at
the same time.
Full-Duplex Transmission
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Signal can travel in both directions at the same
time
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Baseband and
Broadband
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The entire capacity of an Ethernet cable is
used for transmitting the data in one channel.
This makes Ethernet a BASEBAND
technology.
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A channel is an allocated portion of the media’s available
bandwidth.
The signal has the benefit of having the entire bandwidth to
itself.
BASEBAND is usually associated with digital signaling
(although it can be used with analog).
Most computer communications are baseband.
BASEBAND signal is bidirectional; the signal can flow both
ways so you can transmit and receive on the same cable.
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Baseband and
Broadband
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BROADBAND technologies allow for dividing
the capacity of a link into two or more
channels, each of which can carry a different
signal.
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All channels can send simultaneously.
ISDN is an example of BROADBAND technology
because multiple signals can be carried over
separate channels on a single wire.
DSL is another example of a BROADBAND
technology because date and voice can travel
simultaneously over the same line.
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Signaling and
Communications
Problems
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Propagation
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Travel time; speed depends upon medium.
As data transmission rates increase, you must
sometimes take into account the amount of time it takes
the signal to travel.
Attenuation
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Loss of signal over distance due to surroundings.
Can affect a network because it limits the length of
network cabling over which you can send a message.
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Signaling and
Communications
Problems
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Reflection
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Caused by discontinuities in the medium
Occurs in electrical signals; can be result of
kinks in cable or poorly terminated cables.
Networks should have a specific impedance to
match the electrical components in the Network
Interface Cards (NICs).
The result of impedance mismatch is reflected
energy.
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Signaling and
Communications
Problems
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Noise
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Unwanted additions to optical/electromagnetic
signals.
Crosstalk – electrical noise from other wires in a
cable.
EMI (electromagnetic interference) can be caused
by electric motors.
Cancellation of signals can be avoided through the
twisting of wire pairs to provide self-shielding within
the network media.
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Signaling and
Communications
Problems
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Timing problem
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Dispersion – signal broadens in time.
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Jitter – source and destination not
synchronized.
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Can be fixed by proper cable design, limiting cable
lengths, and finding the proper impedance.
Can be fixed through hardware and software
including protocols.
Latency – delay of network signal.
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Signaling and
Communications
Problems
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Collisions
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Occurs when two bits from different
communicating computers are on a shared
medium at the same time.
Excessive collisions can slow the network.
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32
Summary Slide











Parts of an Atom
Types of Electrical Materials
Measuring Electricity
Using a Multimeter to Make Resistance Measurements
Using a Multimeter to Make Voltage Measurements
Signals and Noise in Communication Systems
Measuring Analog Signals
Digital and Analog Signaling
Simplex, Half-Duplex, and Full Duplex Transmission
Baseband and Broadband
Signaling and Communications Problems
Copyright © Texas Education Agency, 2011. All rights reserved.
Computer Maintenance: Electronics/BasicElectricity
33