Transcript Chapter 8 - Goodheart

8
Electrical Engineering
Objectives
• Define electrical engineering.
• Explain the secondary and college level education
requirements for employment in the electrical
engineering profession.
• Explain how electrons move on an atomic level.
• Describe the characteristics of voltage, current,
resistance, and power.
• Explain Ohm’s law and use it to solve for values in a
circuit.
• Identify the operation and application of common
electronic components such as resistors, switches,
capacitors, diodes, and transistors.
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About Electrical Engineering
• Engineering field that deals with electricity and
electronics
• Electrical engineers design, build, and test
electrical devices and facilities
• About 21% of all engineers are electrical engineers
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Educational Requirements
• Bachelor’s degree in electrical engineering
• Higher degrees often required for higher level
positions
• Coursework in electricity, electronics, chemistry,
biology, physics, and higher level math and
statistics
• Associate’s degree required for electrical
technicians
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Professional Organization
• Institute of Electrical and Electronics Engineers
(IEEE)
– Broadest professional society for electrical engineers
– Over 375,000 members
– Dedicated to advancing technological innovation and
excellence through publications, conferences,
standards, and activities
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Electricity on the Atomic Level
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Electrons, protons, neutrons
Valence shell
Electron movement
Electrically charged atoms are called ions
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Static Electricity
• Excess of charge on object’s surface
• Many industrial applications
• Electrostatic precipitator
– Used to remove particles from air
– Charged particles stick to collection plates with
opposite charge
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Electricity Through Conductors
• Negative to positive flow using electron flow theory
• Move slowly, but the effective speed is about the
speed of light
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Sources of Electricity
• Some form of energy is converted into electrical
energy
• Three sources of electricity
– Magnetism
– Chemical action
– Solar cells
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Law of Conservation of Energy
• States that energy cannot be created or destroyed
• Energy can only be converted from one form to
another
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Magnetism
• Generators produce electricity by changing
mechanical energy to electrical energy
• Voltage induced in wire when magnet passes
• Current induced in conductor of generator
• Steam, water, or wind turns turbines, creating
motion that spins generators
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Chemical Action
• Cells use chemical action to create electricity
• Batteries connect multiple cells
• Electrodes of different materials has voltage
created between them
• Two types of cells
– Primary cells
– Secondary cells
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Solar Cells
• Use light to create electricity
• Semiconductors with positive and negative layers
absorb some light energy
• Energy causes electrons to flow in form of current
• Cells can power devices and houses
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Characteristics and Measurements
• Generated electricity has certain characteristics
that can be used in different ways
• Engineers must understand characteristics and
how to measure them
– Voltage
– Current
– Resistance
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Voltage
• Amount of pressure causing flow of electrons
• Expressed as electromotive force (EMF)
• Also called potential difference because it
describes difference in charge from one place to
another
• Measured in volts
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Current
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Measure of electrons per unit time
Also called amperage
Measured in amperes (amps)
One ampere is one coulomb of charge passing a
point in one second
• One coulomb equals 6.24  1018 electrons
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Polarity
• Refers to positive or negative condition at power
supply terminal
• Direct current (dc) occurs when polarity is constant
and current flows in only one direction
• Alternating current (ac) occurs when polarity
changes back and forth from positive to negative,
causing current to change direction
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Resistance
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Opposition to current flow
Measured in ohms (Ω)
Current flow limited and voltage divided by resistors
Resistant materials are insulators
Inversely proportional to current
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Power
• The rate at which work is done or amount of work
done based on period of time
• Electrical power is product of voltage and current
• Measured in watts
• One watt is one volt moving one coulomb of
electricity in one second
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Laws
• Ohm’s law
– Discovered by George Ohm
– Describes relationship between voltage, current, and
resistance
• Watt’s law
– Power equals effort multiplied by rate
– Used to find any one of three values when two are
known
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Basic Circuits
• Series circuits
• Parallel circuits
• Series-parallel combination circuits
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Series Circuits
• One path for current flow
• Total voltage equals sum of drops across all loads
• Total resistance equals sum of resistance of each
load
• Current remains constant throughout
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Parallel Circuits
• Multiple paths for current flow
• Total voltage is equal to the voltage across each
branch
• Total current is equal to the sum of branch currents
1
RT 
1 1 1
 
R1 R 2 R 3
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Series-Parallel Combination Circuits
• Circuits with characteristics of both series and
parallel
• Parallel parts must be broken down and studied as
if they were series elements
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Design
Schematics
• Schematic symbols are used to show components
in circuit drawings
• Schematic diagrams use symbols and lines to
connect components
• Often used in building and troubleshooting circuitry
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Circuit Components
• Each component must be understood
• Understanding is necessary for design and
troubleshooting
• Three main types of components
– Conductors
– Control components
– Output components
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Conductors
• Materials have low resistance
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Copper
Aluminum
Silver
Gold
• Different configurations
• American Wire Gauge (AWG) system determines
size
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Control Components
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Insulators
Resistors
Variable resistors
Switches
Diodes
Zener diodes
• Transistors
• Capacitors
• Integrated circuits
(ICs)
• Semiconductors
• Sensors
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Insulators
• Very high resistance
• Do not conduct electricity under normal
circumstances
• Keep electricity confined to desired path
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Plastic
Rubber
Dry wood/paper
Glass/ceramics
Mica
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Resistors
• Limit current flow and divide voltage
• Most are made from carbon
• Color coding system marks the value of resistors
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Variable Resistors
• Vary amount of resistance in dimmer switches and
fan speed switches
• Two terminals and wiper, which changes amount of
resistive material between terminals
• Represented by arrow symbol
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Switches
• Open and close circuits
• Change direction of flow
• Characterized by type of switch, number of poles,
and number of throws
– SPST switch can turn current on or off to circuit
– SPDT switch can direct current in one direction or
other
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Diodes
• Standard diodes allow current flow in only one
direction
• Have two electrodes
– Anode is made of positive semiconductor material
– Cathode is made of negative semiconductor material
• Current flows in forward bias condition only
• Can be used as rectifiers
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Zener Diodes
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Zener diodes are wired in reverse bias
Block current until voltage reaches certain level
Keep voltage at constant level
Used as voltage regulators
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Transistors
• Used as solid state switches and amplifiers
• Perform switching function without moving parts
• Bipolar transistors have three junction points
– Emitter
– Base
– Collector
• Can also be used as amplifiers
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NPN and PNP Transistors
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Capacitors
• Store and discharge electricity very quickly
• Smooth out variations in voltage
• Two conductive plates separated by thin insulator
called dielectric
• Ceramic disc and electrolytic
• Can maintain charge long after power source is
removed
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Integrated Circuits (ICs)
• Multiple electrical circuits etched into thin layer of
silicon
• Dot or notch on outside of chip is used for
orientation
• Can be sensitive to static
• Common example is 555 timer
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Semiconductors
• Materials with conductive capabilities between that
of conductors and insulators
• Silicon is most common type
• Used in different components
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Transistors
Diodes
Solar panels
Integrated circuits
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Sensors
• Create an electrical signal based on environmental
conditions
• Signal changes as environmental conditions
change
• Common example is electronic thermostats
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Output Components
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Incandescent lamps
Gas discharge lamps
Fluorescent lamps
Compact fluorescent lamps (CFLs)
Light-emitting diode (LED) lamps
Motors
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Incandescent Lamps
• Creates light when current flow causes tungsten
filament to become so hot it glows
• All air inside glass globe is evaluated and
sometimes replaced with argon
• Traditional incandescent bulbs are being phased
out
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Gas Discharge Lamps
• Ionized glass and free electrons cause gas to glow
and create light
• Neon lamps are example, but other gases may be
used
• Resistor must be placed in series with light to limit
current flow
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Fluorescent Lamps
• Long glass tube coated on inside with phosphorous
and filled with inert gas and mercury
• Electrical current passed through mercury causes
ultraviolet light, which causes phosphorous to glow
• Use much less electricity than incandescent lamps
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Compact Fluorescent Lamps (CFLs)
• Work on same principle as fluorescent lamps but fit
into standard light socket
• Use about 75% less energy than incandescent
lamps
• Last up to ten time longer than incandescent lamps
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Light-Emitting Diode (LED) Lamps
• Create light by wiring semiconductor material in
forward biased position
• Forward biased direct current passes through
semiconductor in LED casing, and light is emitted
• Low cost, efficient, and long lasting
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Motors
• Convert electrical energy into mechanical energy
• Electromagnet spins until its north pole lines up
with south pole of permanent magnet
• Polarity of electromagnet reverses, causing it to
keep rotating
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Component Platforms
• Circuit boards
• Solderless breadboards
• Electronic circuit simulation
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Circuit Boards
• Commonly known as printed circuit boards (PCBs)
• Copper track laid on fiberglass
• Electronic components are soldered to copper track
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Solderless Breadboards
• Ideal for experimentation
• Can be used to test circuits before they are
constructed
• Components and leads can easily be added and
removed because no soldering is required
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Electronic Circuit Simulation
• Can be used to simulate performance of circuitry
without having to build circuit
• Components are laid out on-screen
• Software shows how circuits would work
• Problems can be identified early on
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Tools
Meters
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Ammeters
Voltmeters
Ohmmeters
Volt-ohm-milliammeters (VOM)
Continuity tester
Oscilloscope
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Troubleshooting
• First step may be to test voltage
• Continuity tester or ohmmeter may be used to
ensure continuity exists
• Test to see if diode conducts in forward bias and
not reverse
• LEDs can be tested by applying voltage directly
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Electrical Engineering in Action
• Hybrid cars
– Combine internal
combustion engine
and batteries
– Regenerative braking
– Increased fuel mileage
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