Electrical Fundamentals-I
Module 1: Basic Electrical Circuits
PREPARED BY
Academic Services Unit
August 2012
© Institute of Applied Technology, 2012
ATE 310– Electrical Fundamentals-I
Module 1: Basic Electrical Circuits
Module Objectives
Upon successful completion of this module, students should be able to:
1. Define electricity and give an application.
2. Describe the two types of electrical current and give an
application of each.
3. Describe the function and operation of a circuit tester.
4. Describe the function of the four basic components of an
electrical circuit.
5. Describe the operation of two types of power supplies and give
their schematic symbol.
6. Describe the function of an electrical schematic.
7. Describe the operation of a manual switch.
8. Describe the operation of a N.O. and N.C. contacts and give their
schematic symbols.
9. Describe the function of three types of manual switch operators,
give their schematic symbols and an application of each.
10. Describe the function of five types of electrical output devices,
give their schematic symbols and an application of each.
Module Contents:
Topic
Page No.
1.1
Fundamentals of Electricity
3
1.2
Electrical Circuit Components
7
1.3
Manual Input Devices
11
1.4
Output Devices
18
1.5
Lab Activity 1
21
1.6
Lab Activity 2
23
1.7
Lab Activity 3
29
1.8
Review Exercise
34
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1.1 Fundamentals of Electricity
Electricity is defined as the flow of electrons in a conductor. Electrons are very
small, negatively charged particles, which exist in every kind of matter. This
flow of electrons also called current, can deliver energy to a point of use.
Electricity is used for a wide-range of applications including:
•
Lighting
•
Heating/cooling
•
Machine motion (electric motor)
•
Controls (television, radios, computers, etc.)
Figure 1.1: Electrically Powered Manufacturing System
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There are two types of electrical current:
•
Direct Current
•
Alternating Current
Direct Current
Direct current (DC) electricity flows in only one direction, as shown in figure
1.2. Using the conventional theory of current flow, the power supply creates
flow from the highest potential (positive terminal) to the lowest potential
(negative terminal).
Many times the power supply provides both the lowest and the highest
potential points. In figure 1.2, the power supply pushes the electrons through
the conductor and also provides a place for the electrons to return. Any path
that allows the electrons to leave the power supply and return to the power
supply is called a circuit.
Figure 1.2: Direct Current Flow
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A battery is a common source of DC current. Many portable devices operate
on DC current from batteries. Examples include devices such as flashlights,
portable radios, cellular phones, and even laptop computers. Another source
of DC current is DC power supply, which is an electronic circuit that converts
AC current from your wall outlet into DC current. A common use of DC current
sourced from a DC power supply is in a personal computer.
Alternating Current
Alternating current (AC) flows alternately in one direction and then in the
other (cycles). This happens because the power supply pushes the electrons
in one direction for one half of a cycle. It then pushes in the other direction
during the other half of a cycle, as shown in figure 1.3.
Figure 1.3: Alternating Current Flow
Most of the electrical power produced in the world is AC. One reason for this is
that it is easier to transmit over long distances. Another reason is that AC can
be easily changed (transformed) to DC.
AC electricity is used at home, school, and work. The wall outlets at home are
a source of AC for your television set, stereo, microwave, computer, and
other appliances.
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Activity 1. Introduction to Electrical Simulation Software
Perform activity 1 by referring to page-7 of Amatrol-Basic Electrical Circuits
Learning Activity Pack.
1.1.1
Circuit Tester
A circuit tester determines if electricity is present in a circuit. As shown in
figure 1.4, the tester has a tiny neon bulb that glows when current flows
through it. The current flows through the test leads and passes through the
neon bulb.
An example of its use is to test a wall outlet for the presence of AC electricity.
When the leads of the tester are inserted into the outlet, one in the right slot
and the other in the left slot, the neon light should be lit depending on the
presence of electricity (AC).
Figure 1.4: A Common Circuit Tester
Conduct lab activity 1 on page 21.
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1.2 Electrical Circuit Components
An electrical circuit includes the components necessary to deliver the
electricity to the point of use for an application. The four basic components of
an electrical circuit, as shown in figure 1.5, are:
1. Power Supply: This device supplies the energy needed to create an
electrical current.
2. Input Device: This device will allow you to control when the current
will flow in the circuit. Example: switch.
3. Output Device: This component produces a desired output. It is also
referred to as a load. Example: lamp.
4. Conductor: This is the part that connects all the components and
allows current to flow. Copper wire is most often used.
Fig 1.5: The four basic components of an electrical circuit.
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Power supplies are used in electrical systems to modify the power
supplied from the power company (e.g. from the wall socket) to a form that
is needed for the application. One feature power supplies are usually
designed to do is provide a constant current or constant voltage output.
This is called regulation.
A constant current power supply provides the same current level regardless
of the demand placed on it by the load. However, the voltage varies
according to the size of the load. The applications of constant current
power supply are limited, and constant voltage power supplies are more
widely used. They maintain a constant voltage output, regardless of the
load. Here, the current varies instead of the voltage. Constant voltage
supplies come in various forms and can produce AC or DC voltage.
Sometimes they even produce both. The T7017 power supply provides both
constant voltage AC and DC outputs.
Another type of constant voltage DC power supply is a battery. A battery
depends on chemical reaction to produce electricity. It does not require an
external source of power. However, most constant voltage supplies, like the
one shown in figure 1.6, require an external AC power source.
Figure 1.6: Constant voltage power supply
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In addition to regulating voltage or current, power supplies perform other
functions as well. These include reducing voltage levels, changing AC to
DC, and providing overcurrent protection. Figure 1.7 shows the order in
which these functions are performed in the power supply’s circuit.
Figure 1.7: Stages of electrical power supply
Figure 1.8 shows the schematic symbols for a constant voltage AC power
supply and a constant voltage DC power supply.
Figure 1.8: Schematic symbols for a DC power supply and an AC power
supply
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Electrical Diagrams show how the components in a circuit are connected
so that we understand what the circuit does and how it works. While
pictorials allow us to easily see how the devices look, they become very
time consuming to draw and hard to read, especially as circuits become
more complex. Instead, electrical schematic diagrams are used. The
electrical schematic diagram is a form of visual shorthand where each
component is represented by a standard symbol. A schematic diagram
represents the components in a circuit and how they are connected.
However, schematic diagrams do not show physical connections. However,
many schematic diagrams also show certain electrical parameters such as
voltage, current, and resistance values that can be measured at specific
points. This is helpful when you are trying to find a problem in a circuit.
As you progress, you will learn the schematic symbols for each component
you use. Figure 1.9 gives an example of a schematic diagram of a basic
circuit from figure 1.5.
Figure 1.9: Electrical Schematic Diagram for a Basic Electrical Circuit
Conduct lab activity-2 on page-23.
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1.3 Manual Input Devices
A circuit is said to be closed if there is a complete path for current to flow
from the positive terminal to the negative terminal. Figure 1.11 shows a
closed circuit. The path for the current flow is complete so electricity flows
through the lamp.
Fig 1.11: A Closed Circuit.
If the path is broken in some way, the circuit is said to be open. Figure
1.12 shows an open circuit where the current path has been broken. The
current flow is stopped and the lamp is not on.
Fig 1.12: An Open Circuit.
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A simple method for opening and closing a circuit is to use a switch. When
the switch is “closed”, the circuit is closed and electricity flows, as shown in
figure 1.13. When the switch is open, the circuit is also open.
Figure 1.13: Closed and Open Circuits using a switch
The two main components of a manual switch are:
Operator – This component causes the switch to activate.
Contacts – This component will open or close the circuit when the operator
is activated.
Figure 1.14: Components of a Manual Switch
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Switches are commonly used in electrical circuits to control when the power
is supplied to an output device such as a lamp or a machine. With a switch,
you can safely start and stop the current flow.
Switches use two types of contacts:
•
Normally Open (N.O.) – These contacts are open until acted upon by
the operator.
•
Normally Closed (N.C.) – These contacts are closed until acted upon
by the operator.
The schematic symbol for each type is shown in figure 1.15.
Figure 1.15: N.O. and N.C. Contact Symbols.
Activity 2. Switch Operation
Perform activity 3 by referring to the instructions on page-38 of Amatrol-Basic
Electrical Circuits Learning Activity Pack.
The two basic categories of switch operators are:
• Manually-operated - The operator is activated by a person.
• Automatically-operated - The operator is activated by a machine or
other device.
There are several types of manually-operated switches used in electrical
circuits. These switches are even named for their operator. Three of them
are:
• Knife switch
• Pushbutton switch
• Selector switch
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The function of the operator on any manual switch is to allow you to
manually change the states of the contacts of the switch. However, the way
in which each operator does this differs, as you will see in the next
objective.
The applications of the different switches also varies. A knife switch is often
used in applications where a visual confirmation of the switch’s state is
important. A common application is the main disconnect switch for
incoming power to a large machine, like the one shown in figure 1.16.
Figure 1.16: Knife switch used as main disconnect
Pushbutton and selector switches are often used on machine control
panels. Pushbutton switches are frequently used to start and stop a
machine operation. Selector switches are often used to change machine
modes (automatic to manual or forward to reverse).
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Knife Switch
A knife switch, as shown in figure 1.17, consists of a lever (operator) that
conducts current and one or more sets of contacts. When the lever makes
contact with both contacts, the switch is considered closed and allows
electricity to conduct through the circuit. When the lever does not make
contact with both contacts, the switch and the circuit are open. Figure 1.17
also shows the schematic symbols for a knife switch with one set of
contacts, single-pole double-throw (SPDT) and the schematic symbol for a
double-pole double-throw (DPDT) knife switch.
Figure 1.17: A knife switch and its schematic symbols
Pushbutton Switch
A pushbutton switch consists of a pushbutton-type operator and one or
more sets of contacts, as shown in figure 1.18. Pushing the operator
causes the contacts to be opened or closed depending on the normal state.
Most pushbuttons have a set of normally open (N.O.) contacts and a set of
normally closed (N.C.) contacts.
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Figure 1.18: The construction of a Pushbutton Switch
Figure 1.19 shows the schematic symbol of a normally open pushbutton
switch and a normally closed pushbutton switch.
Figure 1.19: Schematic symbols of a Pushbutton Switch
Selector Switch
A selector switch is much like a pushbutton in its design, as shown in figure
1.20. However, instead of pushing a button, you rotate a knob. A selector
switch knob may be designed to stay in a selected position or may have a
momentary action like the pushbutton switch.
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Figure 1.20: The construction of a Selector Switch
Figure 1.21 shows the symbols for a selector switch with normally open
contacts and normally closed contacts.
Figure 1.21: Schematic symbols of a Selector Switch
Conduct lab activity-3 on page-29.
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1.4 Output Devices
There are many types of electrical output devices that can be used in an
electrical circuit. We are going to consider five types:
• Lamp - A lamp or indicator light gives off light when electrical current
flows through its resistive (usually wire) element. They are used on many
pieces of equipment to indicate a certain state of operation. They can
indicate when the power is on, that a certain action is being performed, or
can alert you to a possible danger or problem.
A lamp contains a resistive element inside a glass bulb. The bulb is filled
with a gas. When current flows through the element, the element heats up
and excites the gas. This produces the light that we see. Figure 1.22 shows
the lamp and its schematic symbol.
Figure 1.22: Lamp and its schematic symbol.
Resistor - A resistor limits the flow of electrical current. It is one of the
most commonly used components in an electrical circuit. Resistors are
often used with motors to suppress the surge of current and allow the
current to the motor to be gradually increased. Many electronic devices use
resistors as internal components to control voltages and current.
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A resistor is made of a material that does not allow current to easily flow
through it. The most common material used to make resistors is carbon.
Resistors come in a wide range of values. Figure 1.23 shows a resistor and
its schematic symbol.
Figure 1.23: Resistor and its schematic symbol.
Buzzer - A buzzer is a type of output device that produces sound. Buzzers
are used in doorbells and alarm systems. When electricity is applied to a
buzzer, it causes a vibration to occur inside the buzzer’s housing. This
vibration is what causes the buzzing noise. Figure 1.24 shows a buzzer and
its schematic symbol.
Figure 1.24: Buzzer and its schematic symbol.
Solenoid - A solenoid produces linear mechanical motion from electrical
energy. Solenoids are used to operate flippers in pinball machines, operate
fluid power valves and turn motors on and off. Figure 1.25 shows a
solenoid and its schematic symbol.
Figure 1.25: Solenoid and its schematic symbol.
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The solenoid has an armature or plunger that moves in a linear motion
when electrical current is applied to its electrical coil, as shown in figure
1.26.
Figure 1.26: Construction and operation of a solenoid.
Motor - A motor is the output device that produces rotary mechanical
motion. You see many examples of motors each day. A fan, for example,
uses a motor to turn the blades. When electricity is applied to a motor, a
magnetic field is set up inside it. This magnetic field causes a shaft inside
the motor to start rotating. Whatever is attached to the shaft also rotates.
Figure 1.27: Motor and its schematic symbol.
Conduct lab activity-4 on page-33.
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1.5 Lab Activity 1
Objective:
To use an AC tester to check a wall outlet for electricity.
Safety:
Two basic safety rules to remember when working around electricity are:
1. Avoid touching bare wires or component leads when the power is on.
2. Make sure the power is off before installing, removing, or replacing
components in a circuit.
Electricity does many good things for us, like provide power for our favorite
devices. However, it can also be very dangerous. We don’t need to fear
electricity, but we do need to have a healthy respect for it. It only takes a
small amount of current to cause a severe shock or even death.
Procedure:
1. Locate an electrical wall outlet.
CAUTION
Do not touch the metal part of the test leads while inserting them
into the outlet.
2. Insert one test lead into the left slot of the outlet and the other test
lead into the right slot, as shown in figure 1.28.
Figure 1.28: A common circuit tester
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3. Observe
if
the
indicator
light
is
on.
Indicator
Light
Status
_________(On / Off). It should be on.
4. Now, carefully remove one of the test leads from the outlet. The
indicator light should now be off because you have broken the path
for current to flow through the indicator light. Whenever a circuit
does not provide a complete path for current to flow through, the
circuit is said to be open.
5. Now, carefully insert the test lead back into the slot. The indicator
light should be on again. You have completed the path for current to
flow through the light. The circuit is now closed.
6. Carefully remove both leads from the outlet and store the circuit
tester.
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1.6 Lab Activity 2
Objective:
To identify the components of the T7017 AC/DC Electrical System, and then
connect and operate its power supply.
1. Position yourself in front of the Model T7017 AC/DC Electrical System
shown in figure 1.29.
Figure 1.29: The Model of T7017 AC/DC Electrical Learning System.
2. Locate the Power Cord. This cord plugs into a wall outlet to supply
electricity to the trainer.
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3. Perform the following substeps to locate the various control panel
components on the T7017 AC/DC Electrical System, as shown in figure
1.30.
Figure 1.30: T7017 AC/DC Learning System Control Panel.
4. Locate the Main Power Switch. This switch turns the power on or off for
the entire trainer. Up is the on position. Down is the off position.
5. Locate the Main Power Indicator light. This light will be lit when the
power cord is plugged in and the main power switch is in the on
position. The light will not be lit if the main power switch is in the off
position or if the power cord is not plugged into a wall outlet.
6. Locate the Circuit Breaker. The circuit breaker is a protection device
that protects the trainer from the effects of excessive amounts of
current. You will learn more about the function of a circuit breaker later.
7. Locate the AC/DC Selector Switch. This switch allows you to select
which type of current (direct current or alternating current) is supplied
at the terminals. If the switch is in the left-hand position, AC is
selected. If the switch is in the right-hand position, DC is selected.
8. Locate the AC Indicator Light. This light will be lit when the AC/DC
selector switch is in the left hand (AC) position and the main power is
on.
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9. Locate the DC Indicator Light. This light will be lit when the AC/DC
selector switch is in the right-hand (DC) position and the main power is
on.
10. Locate the Power Supply output terminals. The output terminals provide
a source of either alternating current or direct current. The type of
current supplied and the function of the separate terminals will depend
on the setting of the AC/DC selector switch.
If DC is selected, the right-hand terminal is the positive terminal. This
will be the point from which the current is pushed through whatever
circuit is connected to the power supply. The left-hand terminal is the
negative (return) terminal for the positive terminal if 24 volts is needed.
The center terminal is the return terminal for the positive terminal if 12
volts is needed. This is shown in figure 1.31.
Figure 1.31: Positive, negative and ground terminals for the DC supply.
The center terminal is actually a special return point called a ground. A
ground is usually a common return point for many different circuits. You
will learn more about a ground later. If AC is selected, the polarity of
the terminals is not a factor since the current flow is continuously
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changing directions. Connecting to the right terminal and the left
terminal will provide 24 volts. Connecting to either the left or right
terminal and the center terminal will provide 12 volts.
11. Locate the Analog Voltmeter Display. A voltmeter is an electrical
measurement device. You will learn more about this later.
12. Locate the Voltmeter Test Lead Terminals, as identified in figure 1.31.
The test leads for the voltmeter are connected here. The test leads are
used to perform the measurements.
13. Locate the various component modules. The components are listed
below and shown in figure 1.32. Locate the connection wires and test
equipment included with the T7017, as listed below and shown in figure
1.32.
REF.
A
B
26
DESCRIPTION
Buzzer Module
Capacitor Module
QUANTITY
1
2
C
Circuit Breaker Module
1
D
Magnetic Compass Module
1
E
Fan Module
1
F
Rheostat Module
1
G
H
Fuse Module
DPDT Knife Switch Module
1
1
I
Lamp Module
3
J
Pushbutton Switch Module
1
K
Transformer Module
1
L
M
Relay Module
Selector Switch Module
1
1
N
Solenoid Module
1
O
Resistor Module 10!
1
P
Resistor Module 25!
2
Q
Transformer Load Module
1
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Figure 1.33: Component Modules for the T7017
Locate the connection wires and the test equipment included with the
T7017, as shown in figure 1.34 and listed below.
REF.
DESCR PTION
QUANTITY
R
Test lead pair (Red and Black)
1
S
Digital multimeter
1
T
Neon circuit tester
1
U
Patch cord-spade to spade
1
V
Patch cord-spade to banana
1
Figure 1.34: T7017 Instruments and Connectors.
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1. Perform the following sub steps to connect the power supply.
A. Make sure the main power switch on the front panel of your
trainer is in the OFF position.
B. Carefully plug the main power cord attached to the back of the
trainer into an available wall outlet. Be sure not to touch the
metal prongs on the plug when you insert the plug into the outlet.
C. Observe the power supply output terminals just below the AC-DC
selector switch. You can get different output values (24 or 12)
from the terminals as indicated on the panel. These values are
available for AC or DC output.
2. Perform the following substeps to operate the power supply.
A. Turn on the main power switch. The main power indicator lamp
should be on. If it is not, turn the main power switch OFF and
check to make sure you power cord is properly inserted into the
wall outlet. Then, turn it back on again.
B. Place the AC/DC selector switch in the DC position. The indicator
light above DC should be on.
C. Place the AC/DC selector switch in the AC position. The indicator
light above AC should be on.
3. Perform the following sub steps to shut down the power supply.
A. Turn off the main power switch. All indicator lights should go out.
B. Make sure there are no wires connected to the power supply
output terminals.
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1.7 Lab Activity 3
Objective: To connect and operate three types of manual switches.
Procedure:
1. Position yourself in front of the T7017.
2. Perform the following sub steps to prepare the power supply.
A. Make sure the main power switch is in the OFF position.
B. Place the AC-DC selector switch in the DC position.
C. Make sure there are no wires connected to the output terminals of
the power supply.
3. Connect the circuit shown in figure 1.35. Make sure that the knife
position is as shown. Figure 1.35 shows how to connect the wires to the
terminals.
Figure 1.35: A circuit with a knife switch and a lamp
Notice in figure 1.35, the schematic symbol of a lamp.
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Figure 1.36: How to connect the wires to the terminals on T7017 Electrical
System.
4. Perform the following substeps to operate the circuit.
A. Turn on the main power switch.
B. Close the knife switch and observe the lamp’s status.
Lamp status ______________________________________(On/Off)
The lamp should be on (lighted).
C. Open the knife switch and observe the lamp’s status.
Lamp status _____________________________________(On/Off)
The lamp should be off.
D. Repeat closing and opening the switch a few more times to become
more familiar with it’s operation.
A knife switch is a very basic manually-operated switch. The main
power disconnect switch on a residential or commercial electrical
panel is usually a knife switch.
The knife switch with the T7017 is a double-pole double-throw
(DPDT) switch, which means that it has two sets of contacts. It is
basically the same as having two separate switches in one.
5. Now close the knife switch in the other direction and observe the status
of the lamp. Lamp status ___________________________(On/Off)
The lamp should not be on even though the contacts are closed. This is
because the lamp is not connected to this set of contacts and do not
affect the lamp.
6. Turn off the main power switch. All indicator lights should go out.
7. Disconnect all wires from the components and the power supply
terminals.
8. Connect the circuit represented by the schematic diagram in figure
1.37.
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Figure 1.37: A schematic diagram and pictorial of a circuit with a pushbutton
switch and a lamp.
9. Perform the following substeps to operate the circuit.
A. Turn on the main power switch.
B. Press and hold the pushbutton switch and observe the lamp. Lamp
status ________________________ (On/Off). The lamp should now
be on.
C. Release the pushbutton and observe the lamp. Lamp status
_______________ (On/Off). The lamp should be out.
D. Repeat pressing and releasing the pushbutton a few more times to
familiarize yourself with its operation.
10. Turn off the main power switch.
11. Disconnect the wires connected to the components and the power
supply output terminals.
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12. Connect the circuit represented by the schematic diagram in figure
1.38.
Figure 1.38: A schematic diagram and pictorial of a circuit with a selector
switch and a lamp.
13. Perform the following substeps to operate the circuit.
A. Make sure the selector switch knob is rotated to the left and turn
on the main power switch.
B. Rotate the selector switch to the right and observe the lamp.
Lamp Status___________________________________(On/Off)
The lamp should now be on.
C. Rotate the selector switch in the other direction and observe the
lamp. Lamp status ______________________________(On/Off)
The lamp should go off.
D. Repeat energizing and de-energizing the selector switch a few
more times to familiarize yourself with it’s operation.
Another type of selector switch is the one on the front panel of
your training unit. This switch is used to turn the main power on
and off. Another just like it is used to select between AC or DC
output. These are instrument quality selector switches. They have
a different appearance but operate the same as their industrial
counterparts.
14. Perform the following substeps to turn off and secure the power supply.
A. Turn off the main power switch.
B. Disconnect any wires or components that may be connected to the
power supply output terminals and store them.
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1.8 Review Exercise
Section A:
1. ____________ is the flow of electrons in a conductor.
2. ____________ delivers electrical power to the point of use.
3. A device that creates electrical current is a(n) _____________________.
4. The flow of electricity in only one direction is called _______________
current.
5. A common source of DC is a(n) _________________.
6. The flow of electrons in one direction and then the other direction is
called ______________ current.
7. The output from an electrical wall outlet is _____________ current.
8. A(n) ____________________ uses a tiny neon bulb that glows when
current flows through it.
9. A common input device is a(n) _________________.
10. An output device is also called a(n) ___________________.
11. A(n) __________________ connects all of the components in an
electrical circuit.
12. Electrical ______________ diagrams are forms of visual shorthand
where each component is represented by a standard symbol.
13. A constant _________________ power supply maintains the same
output voltage regardless of the load connected to it.
14. A battery depends on a(n) ____________ reaction to product electricity.
15. A simple method for opening and closing a circuit is to use a(n)
_____________.
16. The two main components of a switch are the ________________ and
the contacts.
17. The two basic categories of electrical switches are manual and
__________________.
18. If the path is broken in some way, the circuit is said to be
____________.
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19. A(n)
_________________
makes
a
manually-operated
switch
momentary.
20. A(n) ___________________ produces mechanical linear motion.
21. A resistor will give off ___________________.
22. A buzzer will give off ____________________.
23. A motor is an output device that produces _________________
mechanical motion.
Section B:
1.
Draw the symbols of the ‘Normally Open’ and the ‘Normally Closed
switch’.
2.
The motor of a mixer needs to be operated in three different power
levels 1, 2 and 3. Name the type of switch that could be used for this
purpose.
__________________________________________________________
3.
Give examples of the application of buzzers.
__________________________________________________________
__________________________________________________________
4.
Name the type of output device that produces linear mechanical motion
and can be used to operate fluid power valves.
__________________________________________________________
34
Module 1: Basic Electrical Circuits