ac.dc.electrical,systems

BASIC ELECTRICAL CIRCUITSBASIC ELECTRICAL CIRCUITS

LEARNINGACTIVITYPACKET

B227-AC

AC/DCELECTRICALSYSTEMS

TM

LEARNING ACTIVITY PACKET 1

BASIC ELECTRICAL CIRCUITS

INTRODUCTIONElectricity is used to perform tasks related to almost everything we do. In this unit,

you are going to learn the fundamental concepts of electricity used in many applications,especially control systems. The specific skills you learn will enable you to perform basicelectrical projects at home and on the job. These skills will also be applied in many otherunits including programmable controllers, electrical motor control, and electro-fluidpower.

In this LAP, you will learn how a basic electrical circuit works by setting up anumber of circuits using the various components in the Amatrol T7017 AC/DC Electrical Learning System. This will also help you get more familiar with the operation of thetrainer you will be using.

ITEMS NEEDEDAmatrol Supplied 1 T7017 AC/DC Electrical Learning System 1 94-CBT-E1 Electrical Simulation Software

School Supplied 1 Computer

B227-AC LAP 1 BASIC ELECTRICAL CIRCUITSCopyright 2005 Amatrol, Inc. 2

de ee dN smetI

FIRST EDITION, LAP 1, REV. BAmatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST and Technovate are trademarks or registeredtrademarks of Amatrol, Inc. All other brand and product names are trademarks or registered trademarks of theirrespective companies.Copyright 2005 by AMATROL, INC.All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by anymeans, electronic, optical, mechanical, or magnetic, including but not limited to photographing, photocopying,recording or any information storage and retrieval system, without written permission of the copyright owner.Amatrol,Inc., P.O. Box 2697, Jeffersonville, IN 47131 USA, Ph 812-288-8285, FAX 812-283-1584 www.amatrol.com

TABLE OF CONTENTS

SEGMENT 1 FUNDAMENTALS OF ELECTRICITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4OBJECTIVE 1 Define electricity and give an applicationOBJECTIVE 2 Describe the two types of electrical current and give an application of each

Activity 1 Introduction to electrical simulation softwareOBJECTIVE 3 Describe the function and operation of a circuit tester

SKILL 1 Use an AC tester to check a wall outlet for electricity

SEGMENT 2 ELECTRICAL CIRCUIT COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20OBJECTIVE 4 Describe the function of the four basic components of an electrical circuit

Activity 2 Basic circuit operationOBJECTIVE 5 Describe the operation of two types of power supplies and give their schematic symbolsOBJECTIVE 6 Describe the function of an electrical schematic

SKILL 2 Connect and operate a power supply

SEGMENT 3 MANUAL INPUT DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35OBJECTIVE 7 Describe the operation of a manual switchOBJECTIVE 8 Describe the operation of N.O. and N.C. contacts and give their schematic symbols

Activity 3 Switch operationOBJECTIVE 9 Describe the function of three types of manual switch operators and give an application of eachOBJECTIVE 10 Describe the operation of three types of manual switch operators and give their schematic symbols

SKILL 3 Connect and operate a circuit using three types of manual switches

SEGMENT 4 OUTPUT DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52OBJECTIVE 11 Describe the function of five types of electrical output devices and give an application of eachOBJECTIVE 12 Describe the operation of five types of electrical output devices and give their schematic symbols

SKILL 4 Connect and operate an electrical circuit with a resistorSKILL 5 Connect and operate an electrical circuit with a buzzerSKILL 6 Connect and operate an electrical circuit with a solenoidSKILL 7 Connect and operate an electrical circuit with a motor


SEGMENT 1

FUNDAMENTALS OF ELECTRICITY

OBJECTIVE 1 DEFINE ELECTRICITY AND GIVE AN APPLICATION

Electricity is defined as the flow of electrons in a conductor.Electrons are very small, negatively-charged particles which exist inevery kind of matter.

This flow of electrons, also called current, can deliver energy to apoint of use.

Electricity is used for a wide range of applications including: Lighting Heating/cooling Machine motion (electric motor) Controls (televisions, radios, computers, etc.)


Figure 1. Electrically-Powered Manufacturing System

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OBJECTIVE 2 DESCRIBE THE TWO TYPES OF ELECTRICAL CURRENTAND GIVE AN APPLICATION OF EACH

There are two types of electrical current: Direct Current Alternating Current

Direct CurrentDirect current (DC) electricity flows in only one direction, as shown

in figure 2. Using the conventional theory of current flow, the powersupply creates flow from the highest potential (positive terminal) to thelowest potential (negative terminal).

Many times the power supply provides both the lowest and highestpotential points. In figure 2, the power supply pushes the electronsthrough the conductor and also provides a place for the electrons toreturn. Any path that allows the electrons to leave the power supply andreturn to the power supply is called a circuit.

A battery is a common source of DC current. Many portable devicesoperate on DC current from batteries. Examples include devices such asflashlights, portable radios, cellular phones, and even laptop computers.

Another source of DC current is a DC power supply, which is anelectronic circuit that converts AC current from your wall outlet into DCcurrent. A common use of DC current sourced from a DC power supplyis in a personal computer.


POWERSUPPLY

+ -

(HIGHESTPOTENTIAL)

POSITIVETERMINAL

CONVENTIONALDIRECTION OF

CURRENTFLOW

(LOWESTPOTENTIAL)NEGATIVETERMINAL

PUSH

CONDUCTOR

LOAD

Figure 2. Direct Current (DC) Current Flow

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Alternating CurrentAlternating current (AC) flows alternately in one direction and then

in the other (cycles). This happens because the power supply pushes inone direction for one-half of a cycle. It then pushes in the other directionduring the other half of a cycle, as shown in figure 3.

Most of the electrical power produced in the world is AC. Onereason for this is that it is easier to transmit over long distances. Anotherreason is that AC can be easily changed (transformed) to DC.

AC electricity is used at home, school, and work. The wall outlets athome are a source of AC for your television set, stereo, microwave,computer, and other appliances.


POWERSUPPLY

FIRST HALF OF A CYCLE SECOND HALF OF A CYCLE

CURRENTFLOW

PUSH PUSH

CONDUCTOR CONDUCTOR

POWERSUPPLY

Figure 3. Alternating Current (AC) Current Flow

NOTEThe AC electricity produced in the United States cycles 60

times per second.

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Activity 1. Introduction to Electrical Simulation Software

q 1. Turn on the computer that has the electrical simulation softwareand allow it to boot up.

q 2. Perform the following substeps to start the electrical simulationsoftware.A. Click on Start. B. Click on All Programs.C. Select the Edison folder. D. Click on the Edison icon as shown in figure 4.


Procedure OverviewIn this procedure, you will use an electrical simulation

software package to help demonstrate the concept ofelectricity.

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Figure 4. Edison Software Folder

After a few seconds, the simulation screen should appear, asshown in figure 5.

q 3. Perform the following substeps to identify the areas of theelectrical simulation screen.A. If the simulation screen is not shown full screen, move the

pointer to the maximize button and click the left mouse buttonto cause the window to become full screen.The Minimize, Maximize/Restore, and Close buttons arelocated at the top right corner of the window, as identified infigure 6.

B. Move the pointer to the Menu bar.The Menu bar contains commands that allow you to performtasks such as manipulating files, changing simulation settings,opening existing experiment or problem files, and accessingon-screen help.

C. Move the pointer to the Circuit Construction Surface.The construction surface is the part of the screen whereelectrical circuits are constructed.

D. Move the pointer to the Component Shelves (left and right).The component shelves, located on each side of theconstruction surface, contain the components that can be usedto construct electrical circuits.


Figure 5. Simulation Screen

MENUBAR

RIGHTCOMPONENT

SHELF

LEFTCOMPONENT

SHELF

CIRCUITCONSTRUCTION

SURFACE

CLOSE

MINIMIZERESTORE/MAXIMIZE

q 4. Perform the following substeps to create an electrical circuit. A. Move the pointer to the square battery, as shown in figure 6.

B. Click the left mouse button to select the square battery.C. Move the battery to the construction surface.

As you move the mouse, you should see the battery moveacross the screen. If the battery does not move, go back andclick on it again. Then, try to move it again.

D. When the battery is located near the center of the constructionarea, click the left mouse button to place the battery on theconstruction surface, as shown in figure 7.


Figure 6. The Square Battery

Figure 7. The Battery on the Construction Surface

SQUAREBATTERY

LAMPS

E. Move the pointer to the medium-power lamp and repeatsubsteps B-D to place the lamp on the construction surface, asshown in figure 8.


Figure 8. The Medium-Power Lamp Placed on the Construction Surface

NOTEEach of the three lamps has a different power rating. The

low-power lamp has a 2-watt power rating. The medium-powerlamp has a 3-watt power rating, and the high-power lamp has a15-watt power rating.

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LOW POWER

MEDIUM POWER

HIGH POWER

MEDIUMPOWERLAMP

F. Move the pointer to the positive (+) connection post for thebattery, as shown in figure 9. The pointer should change to a terminal symbol. This tells youthat you can now connect a wire to the selected terminal.

G. Click the left mouse button to connect a wire to the selectedterminal.


Figure 9. Connection Terminal Selected

H. Now, move the pointer to the connection terminal on the leftside of the lamp base. As you move the mouse, you should notice a wire is extendingfrom the connection post on the battery and is following behind the pointer. The terminal indicator will again appear when the pointer isover the terminal on the lamp, as shown in figure 10.

I. Click the left mouse button again to attach the wire to the leftconnection post of the lamp.


Figure 10. Wire Connected from the (+) Post of the Battery to the LeftPost of the Lamp

J. Repeat substeps F-I to connect a wire from the negative (-)connection post of the battery to the right connection post ofthe lamp, as shown in figure 11.Notice that the lamp has changed colors to indicate that it isnow lit. The battery is now pushing electrons through theavailable path. This results in a current flow through the wiresand the lamp, which causes the bulb to light up. Current leaves one post of the battery, travels through the lamp, and returns to the other post of the battery.You will learn later why the lamp lights up when current passes through it.


Figure 11. Connections Completed

q 6. Perform the following substeps to shut down the electricalsimulation software. A. Click on File.

A drop-down menu will appear, as shown in figure 12.


Figure 12. File Drop-Down Menu

B. Click on Exit .A prompt box will appear in the center of the screen, as shownin figure 13.

C. Select No. This closes the electrical simulation software without savingthe circuit that you created. There is no need to save the circuit.


Figure 13. Prompt Box

OBJECTIVE 3 DESCRIBE THE FUNCTION AND OPERATIONOF A CIRCUIT TESTER

A circuit tester determines if electricity is present in a circuit. Asshown in figure 14, the tester has a tiny neon bulb that glows whencurrent flows through it. The current flows through the test leads andpasses through the neon bulb.

An example of its use is to test a wall outlet for the presence of ACelectricity. 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 ifthere is AC electricity present.


FOR TESTING

CRICUITS

NEON LIGHT

TESTLEADS

CIRCUITTESTER

WALLOUTLET

HOW TO USE A CIRCUIT TESTER

Figure 14. A Common Circuit Tester

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SKILL 1 USE AN AC TESTER TO CHECK A WALL OUTLETFOR ELECTRICITY

q 1. Locate an electrical wall outlet.


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Procedure OverviewIn this procedure, you will test a wall outlet for the

presence of AC current using a circuit tester.

CAUTIONDo not touch the metal part of the test leads while inserting

them into the outlet.

CAUTION

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CAUTIONTwo 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 dont need to fear electricity, but we do need to have ahealthy respect for it. It only takes a small amount of current tocause a severe shock or even death.

CAUTION

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q 2. Insert one test lead into the left slot of the outlet and the other testlead into the right slot, as shown in figure 15.

q 3. Observe if the indicator light is on.Indicator Light Status____________________________(On / Off)It should be on.

q 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 toflow through, the circuit is said to be open.

q 5. Now, carefully insert the test lead back into the slot. The indicatorlight should be on again.You have completed the path for current to flow through the light.The circuit is now closed.

q 6. Carefully remove both leads from the outlet and store the circuittester.


Figure 15. A Common Circuit Tester

SEGMENT 1 SELF REVIEW


hT ir sewsnA1. __________ 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 called a__________ __________.

4. The flow of electricity in only one direction is called__________ current.

5. A common source of DC is a __________.

6. The flow of electrons in one direction and then the otherdirection is called __________ current.

7. The output from an electrical wall outlet is _________current.

8. A _________ _________ uses a tiny neon bulb that glowswhen current flows through it.

SEGMENT 2

ELECTRICAL CIRCUIT COMPONENTS

OBJECTIVE 4 DESCRIBE THE FUNCTION OF THE FOUR BASICCOMPONENTS OF AN ELECTRICAL CIRCUIT

An electrical circuit includes the components necessary to deliver the electricity to the point of use for an application. The four basiccomponents of an electrical circuit, as shown in figure 16, are:

Power supply - This device supplies the energy needed to createan electrical current.

Input device - This is the part that allows you to control when thecurrent will flow in a circuit. A common input device is a switch.

Output device - This component produces a desired output. It isalso referred to as a load. A common output device is a lamp.

Conductor - This is the part that connects all the components andallows current to flow. Copper wire is most often used.

You will learn more about each of these components as you progress through the rest of this LAP.


CONDUCTOR

(OUTPUT DEVICE)INDICATOR

LAMP

(INPUT DEVICE)SWITCH

(POWER SUPPLY)BATTERY

Figure 16. The Four Basic Components of an Electrical Circuit

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Activity 2. Basic Circuit Operation

q 1. Turn on the computer that has the electrical simulation software.q 2. Perform the following substeps to start the electrical simulation

software.A. Click on Start.B. Select All Programs.C. Select the folder Edison.D. Click on the Edison icon.

After a few seconds, the simulation screen should appear.q 3. Perform the following substeps to construct the circuit shown in

figure 17.


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Procedure OverviewIn this procedure, you will use the electrical simulation

software to construct an electrical circuit that includes thefour basic circuit components. You will then simulate theoperation of the circuit to help you understand theoperation of the electrical circuit.

Figure 17. A Basic Electrical Circuit

A. Select the square battery from the left component shelf. Remember, to select an item, simply move the pointer to thatitem and click the left mouse button.

B. Move the battery to the center of the construction surface. C. Click the left mouse button to place the battery onto the

construction surface. D. Select the medium-power lamp from the left component shelf

and place it on the construction surface.E. Select the upper pushbutton switch from the right component

shelf, as shown in figure 18.

F. Place the switch on the construction surface.G. Run wires between the components to create the circuit shown

in figure 17.


Figure 18. Upper Pushbutton Switch

UPPERPUSHBUTTON

SWITCH

q 4. Perform the following substeps to simulate the operation of thiscircuit. A. Move the pointer over the switch, as shown in figure 19.

B. Click the left mouse button. The center of the switch should move down as if you werepressing it with your finger. This closes the circuit by providing a continuous path for current to flow. The battery can push thecurrent through the circuit and cause the lamp to light up, asshown in figure 20.


Figure 19. The Pointer Over the Switch

Figure 20. The Switch Allows the Current to Flow Through the Circuit

C. Move the pointer over the switch again and click the left mouse button. The center of the switch will pop back up, opening the circuit.The lamp is no longer lit. The battery can no longer pushcurrent through the circuit because the opened switch is nowblocking the current.

D. Repeat substeps B and C a few more times to become morefamiliar with the operation. In this case, the battery (power supply) provides the force topush the electrons through the circuit. However, the switchcontrols when the battery can push the electrons through thecircuit. You will learn how the switch performs this operation later inthis LAP.

q 5. Perform the following substeps to shut down the electricalsimulation software. A. Move the pointer to the File selection on the menu bar and

click the left mouse button to select it. The file drop-down menu will appear.

B. Move the pointer to the Exit selection and click the left mousebutton to select it. A prompt box will appear in the center of the screen.

C. Move the pointer to the No button in the prompt box and clickthe left mouse button to select it. This closes the electrical simulation software without savingthe circuit that you created. There is no need to save the circuit.


OBJECTIVE 5 DESCRIBE THE OPERATION OF TWO TYPES OF POWERSUPPLIES AND GIVE THEIR SCHEMATIC SYMBOLS

Power supplies are used in electrical systems to modify the powersupplied from the power company (e.g. from the wall socket) to a formthat 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 supply provides the same current level regardlessof the demand placed on it by the load. However, the voltage variesaccording to the size of the load.

The applications of a constant current supply are limited. They aremost often used to supply a specific current in process control circuits,where a constant current level is critical to the operation.

Constant voltage power supplies are more widely used. Theymaintain a constant voltage output, regardless of the load. Here, thecurrent varies instead of the voltage.

Constant voltage supplies come in various forms and can produceAC or DC voltage. Sometimes they even produce both. The T7017power supply provides both constant voltage AC and DC outputs.


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Another type of constant voltage DC power supply is a battery. Abattery depends on a chemical reaction to produce electricity. It doesntrequire an external source of power. However, most constant voltagesupplies, like the one shown in figure 21, require an external AC powersource.

In addition to regulating voltage or current, power supplies performother functions as well. These include reducing voltage levels, changingAC to DC, and providing overcurrent protection.

Figure 22 shows the order in which these functions are performed inthe power supplys circuit.


Figure 21. Constant Voltage Power Supply

CHANGESVOLTAGE

LEVEL

CONVERTSINCOMING

POWERFROM AC

TO DC

REGULATESOUTPUT

OVERCURRENTPROTECTION

INCOMINGVOLTAGE

CONVERTEDOUTPUTVOLTAGESTAGE 1 STAGE 2 STAGE 3 STAGE 4

ELECTRICAL POWER SUPPLY

Figure 22. Stages of an Electrical Power Supply

CONNECTION TO AC POWER SOURCE

Figure 23 shows the schematic symbols for a constant voltage ACpower supply and a constant voltage DC power supply.

OBJECTIVE 6 DESCRIBE THE FUNCTION OF AN ELECTRICAL SCHEMATIC

Electrical diagrams show how the components in a circuit areconnected so that we can understand what the circuit does and how itworks. So far the diagrams used have been pictorial, where actualpictures are used. While pictorials allow us to easily see how the deviceslook, 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 schematicdiagram (sometimes called a wiring diagram) shows all the componentsin a circuit and how they are connected. Many schematic diagrams evenshow certain electrical parameters such as voltage, current, andresistance values that can be measured at specific points. This is helpfulwhen you are trying to find a problem in a circuit.

As you progress, you will learn the schematic symbols for eachcomponent you use. Figure 24 gives an example of a schematic diagramof the basic circuit from figure 16.


DC POWER SUPPLY

+ -

AC POWER SUPPLY

Figure 23. Schematic Symbols for a DC Power Supply and an AC Power Supply

LAMP

DC POWER SUPPLY

+

SWITCH

Figure 24. Electrical Schematic Diagram of a Basic Electrical Circuit

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SKILL 2 CONNECT AND OPERATE A POWER SUPPLY

q 1. Position yourself in front of the Model T7017 AC/DC ElectricalSystem shown in figure 25.

q 2. Locate the Power Cord.This cord plugs into a wall outlet to supply electricity to thetrainer.


POWERCORD

Figure 25. The Model T7017 AC/DC Electrical System

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Procedure OverviewIn this procedure, you will first identify the components

of the T7017 AC/DC Electrical System. You will thenconnect and operate its power supply.

q 3. Perform the following substeps to locate the various control panelcomponents on the T7017 AC/DC Electrical System, as shown infigure 26.

A. Locate the Main Power Switch.This switch turns the power on or off for the entire trainer. Upis the on position. Down is the off position.

B. Locate the Main Power Indicator light.This light will be lit when the power cord is plugged in and themain 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 powercord is not plugged into a wall outlet.

C. Locate the Circuit Breaker.The circuit breaker is a protection device that protects thetrainer from the effects of excessive amounts of current. Youwill learn more about the function of a circuit breaker later.

D. Locate the AC/DC Selector Switch. This switch allows you to select which type of current (directcurrent or alternating current) is supplied at the terminals. If the switch is in the left-hand position, AC is selected. If the switchis in the right-hand position, DC is selected.

E. Locate the AC Indicator Light.This light will be lit when the AC/DC selector switch is in theleft-hand (AC) position and the main power is on.


MAIN POWERINDICATOR

AC/DC SELECTORSWITCH

ANALOG VOLTMETERDISPLAY

CIRCUITBREAKER

POWER SUPPLYOUTPUT TERMINALS

VOLTMETERTEST LEADTERMINALS

MAINPOWERSWITCH

AC INDICATORLIGHT

DC INDICATORLIGHT

Figure 26. Control Panel of the T7017 AC/DC Electrical System

F. Locate the DC Indicator Light.This light will be lit when the AC/DC selector switch is in theright-hand (DC) position and the main power is on.

G. Locate the Power Supply Output Terminals.The output terminals provide a source of either alternatingcurrent or direct current. The type of current supplied and thefunction of the separate terminals will depend on the setting ofthe AC/DC selector switch. If DC is selected, the right-hand terminal is the positiveterminal. This will be the point from which the current ispushed through whatever circuit is connected to the powersupply. The left-hand terminal is the negative (return) terminalfor the positive terminal if 24 volts is needed. The centerterminal is the return terminal for the positive terminal if 12volts is needed. This is shown in figure 27.

The center terminal is actually a special return point called aground. A ground is usually a common return point for manydifferent circuits. You will learn more about a ground later. If AC is selected, the polarity of the terminals is not a factorsince the current flow is continuously changing directions.Connecting to the right terminal and the left terminal willprovide 24 volts. Connecting to either the left or right terminaland the center terminal will provide 12 volts.

H. Locate the Analog Voltmeter Display.A voltmeter is an electrical measurement device. You will learn more about this later.


SOURCE SELECT

AC DC

12V 12V24V

GROUND

(-)(-) (+)

Figure 27. Positive, Negative, and Ground Terminals for the DC Supply

I. Locate the Voltmeter Test Lead Terminals, as identified infigure 27.The test leads for the voltmeter are connected here. The testleads are used to perform the measurements.

q 4. Locate the various component modules. The components are listed below and shown in figure 28.


Figure 28. Component Modules for the T7017

M.

O.G.

E. D.

I.

H.

J.

K.

C. N. P.L.

B. A.F.

REF. DESCRIPTION QTY.A. Lamp Module 3B. DPDT Knife Switch Module 1C. Capacitor Module 2D. Solenoid Module 1E. Relay Module 1F. Fuse Module 1G. Resistor Module 25 Ohm 2H. Resistor Module 10 Ohm 1I. Rheostat Module 1J. Pushbutton Switch Module 1K. Selector Switch Module 1L. Circuit Breaker Module 1M. Transformer Module 1N. Buzzer Module 1O. Fan Module 1P. Magnetic Compass Module 1

q 5. Locate the connection wires and test equipment included with theT7017, as listed below and shown in figure 29.


NOTEIf any of these components are not present, notify your

instructor.

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Figure 29. T7017 Instruments and Connectors

REF. DESCRIPTION QTY.Q. Test Lead Pair, 1 Red/1 Black 1R. Digital Handheld Multimeter 1S. Neon Circuit Tester 1T. Patch Cord-Spade to Spade 10U. Patch Cord-Spade to Banana 4

Q.R. T.

U.S.

q 6. Perform the following substeps 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 youinsert the plug into the outlet.

C. Observe the power supply output terminals just below theAC-DC selector switch.You can get different output values (24 or 12) from theterminals as indicated on the panel. These values are availablefor AC or DC output.

q 7. 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, turnthe main power switch OFF and check to make sure you powercord is properly inserted into the wall outlet. Then, turn it backon again.

B. Place the AC/DC selector switch in the DC position. Theindicator 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.

q 8. Perform the following substeps 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.




hT ir sewsnA1. A common input device is a _________.

2. An output device is also called a __________.

3. A __________ connects all of the components in anelectrical circuit.

4. __________ diagrams are forms of visual shorthand whereeach component is represented by a standard symbol.

5. A constant __________ power supply maintains the sameoutput voltage regardless of the load connected to it.

6. A battery depends on a __________ reaction to productelectricity.

SEGMENT 3

MANUAL INPUT DEVICES

OBJECTIVE 7 DESCRIBE THE OPERATION OF A MANUAL SWITCH

A circuit is said to be closed if there is a complete path for current toflow from the positive terminal to the negative terminal. Figure 30 shows a closed circuit. The path for the current flow is complete so electricityflows through the lamp.


LAMP(ON)

BATTERY

CONDUCTORWIRE

CURRENT FLOW

Figure 30. A Closed Circuit

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If the path is broken in some way, the circuit is said to be open.Figure 31 shows an open circuit where the current path has been broken.The current flow is stopped and the lamp is not on.

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 32. When the switch is open the circuit is also open.


LAMP

BATTERY

(WIRE)

(OFF)

CONDUCTOR

BROKENPATH

Figure 31. An Open Circuit

INDICATOR LAMP

CLOSED CIRCUIT OPEN CIRCUIT

(CLOSED)SWITCH (OPEN)SWITCH

CURRENTFLOWS

Figure 32. Closed and Open Circuits Using a Switch

The two main components of a manual switch are the: Operator - This component causes the switch to activate. Contacts - This component will open or close the circuit when

the operator is activated.

Switches are commonly used in electrical circuits to control whenthe power is supplied to an output device such as a light or a machine.With a switch, you can safely start and stop the current flow.

OBJECTIVE 8 DESCRIBE THE OPERATION OF N.O. AND N.C. CONTACTSAND GIVE THEIR SCHEMATIC SYMBOLS

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 34.


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NORMALLYOPEN

NORMALLYCLOSED

Figure 34. N.O. and N.C. Contact Symbols

OPERATOR

CONTACTS

KNIFE SWITCH

Figure 33. Components of a Manual Switch

Activity 3. Switch Operation

q 1. Start the Edison software. q 2. Select the middle pushbutton switch from the right component

shelf and place it on the construction surface. This switch is a normally open (N.O.) switch.

q 3. Perform the following substeps to connect the circuit shown infigure 35.

A. Select the square battery and place it on the constructionsurface.

B. Select the medium-power lamp and place it on theconstruction surface.

C. Connect a wire from the positive (+) terminal of the battery tothe left terminal of the switch.

D. Connect a wire from the right terminal of the switch to the leftterminal of the bulb.

E. Connect a wire from the right terminal of the bulb to thenegative (-) terminal of the battery.


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Procedure OverviewIn this procedure, you will use the electrical simulation

software to learn more about the operation of N.O. andN.C. contacts. You will see how the status of the switchoperator affects the state of the contacts.

Figure 35. Circuit with N.O. Switch

MIDDLEPUSHBUTTON

SWITCH

q 4. Perform the following substeps to operate the N.O. switch. When a switch with a normally open contact is in its normal (notactivated) state, the contacts will be open. It will not allow currentto pass.When the switch is activated or energized, (operator pressed) the contacts close, allowing current to pass. Figure 36 shows the twostates.Since the normally open contacts are being used, the switch is alsodescribed as normally open.

A. Move the pointer over the switch operator. Then click and holdthe left mouse button. The operator should activate causing the N.O. contacts to close, and allowing current to flow.

B. Now, release the mouse button.The switch should now deactivate allowing the contacts toopen.The operation of this switch differs from the switch you used in activity 2. That switch, which also had N.O. contacts, wouldremain activated until you pressed the operator again. A switchthat remains activated after you release the operator is called amaintained switch. The switch you are using in this activity is called a momentaryswitch because it does not remain in its activated state whenyou release the operator. A spring causes the operator to returnto its normal position. Many pushbutton switches used inmachine control are momentary switches.

C. Repeat substeps A and B to become more familiar with theoperation of the momentary N.O. Switch.


LAMP

POWER

OPEN

PUSHBUTTON

SUPPLYDC

(OFF)LAMP

POWER

CLOSED

PUSHBUTTON

SUPPLYDC

(ON)

+ +- -

PUSHBUTTON INNORMAL STATE

PUSHBUTTON INACTIVATED STATE

Figure 36. A Normally Open Switchs States of Operation

q 5. Perform the following substeps to remove the circuit from theconstruction surface. A. Select File from the menu bar. B. Select New from the File drop-down menu. C. When the save file prompt box appears, select the No button.

The file will not be saved. q 6. Connect the circuit shown in figure 37.

For this circuit, you will use the lower pushbutton switch.

The switch that you are using in this circuit has both N.O. andN.C. contacts, as figure 38 shows. The connection post on theupper left side of the switch is called a common terminal. Someswitches that contain multiple sets of contacts have a commonconnection point for the N.O. and N.C. contacts.This circuit is similar to the circuit you constructed earlier.However, this circuit is connected through the N.C. contacts of theswitch. For this reason, the operation of the circuit will be different than the circuit you constructed earlier.


Figure 37. Circuit with a Switch which has Both N.O. and N.C. Contacts

N.C.N.O.

COMMON

LOWERPUSHBUTTON

SWITCH

Normally closed (N.C.) contacts operate just the opposite ofnormally open contacts. N.C. contacts are closed when the switchis not activated (in its normal state). Activating the switch causesthe contacts to open, as shown in figure 38.

q 7. Move the pointer over the pushbutton switch and click the leftmouse button to activate the switch. The lamp should now be off because the contacts have changed tothe energized state (open).

q 8. Move the pointer over the pushbutton switch and click the leftmouse button again. The lamp should be on again because the contacts have returned to their normal state (closed).


LAMP

POWER

OPEN

PUSHBUTTON

SUPPLYDC

(OFF)LAMP

POWER

CLOSED

PUSHBUTTON

SUPPLYDC

(ON)

++ --

NORMAL STATE ACTUATED STATE

Figure 38. A Normally Closed Switchs States of Operation

NOTEIt is important to understand that there is a difference between

open/closed and energized/deenergized. If a switch is energized,this only means that the switchs operator is activated. It does notmean that the switch is necessarily closed. Whether the switch isopen or closed when activated depends on its normal state.

hT i secitoN

q 9. Add another lamp to the circuit, as shown in figure 39.The extra lamp is connected to the N.O. contact of the switch.

q10. Perform the following substeps to operate the circuit. A. Move the pointer over the pushbutton switch and click the left

mouse button. The first lamp should now be off and the second lamp shouldbe on. The N.C. contacts are in their energized states (open).The N.O. contacts are also in their energized states (closed). As you can see, switches with multiple sets of contacts cancontrol more that one circuit at the same time. This switch wasable to turn on one lamp while turning off another at the sametime.

B. Move the pointer over the pushbutton switch and click the leftmouse button again. Now, the first lamp should be on and the second lamp shouldbe off. The contacts have returned to their normal states.

C. Repeat substeps A and B a few more times to become morefamiliar with the operation of the contacts.

q11. Perform the following substeps to exit the software. A. Select File from the menu bar. B. Select Exit from the File pull-down menu. C. When the save file prompt box appears, select the No button.

The file will not be saved. The software will return to the Windows desktop.

q12. Exit Windows and shut down the computer.


Figure 39. Another Lamp Added to the Circuit

N.O.

COMMON

ANOTHERLAMP

N.C.

OBJECTIVE 9 DESCRIBE THE FUNCTION OF THREE TYPES OF MANUALSWITCH OPERATORS AND GIVE AN APPLICATION OF EACH

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 switchThe function of the operator on any manual switch is to allow you to

manually change the states of the contacts of the switch. However, theway in which each operator does this differs, as you will see in the nextobjective.

The applications of the different switches also varies. A knife switchis often used in applications where a visual confirmation of the switchsstate is important. A common application is the main disconnect switchfor incoming power to a large machine, like the one shown in figure 40.

Pushbutton and selector switches are often used on machine controlpanels. Pushbutton switches are frequently used to start and stop amachine operation.

Selector switches are often used to change machine modes(automatic to manual or forward to reverse).


Figure 40. Knife Switch Used as Main Disconnect

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DISCONNECTSWITCH

OBJECTIVE 10 DESCRIBE THE OPERATION OF THREE TYPES OF MANUALSWITCH OPERATORS AND GIVE THEIR SCHEMATIC SYMBOLS

Knife SwitchA knife switch, as shown in figure 41, consists of a lever (operator)

that conducts current and one or more sets of contacts. When the levermakes contact with both contacts, the switch is considered closed andallows electricity to conduct through the circuit. When the lever does not make contact with both contacts, the switch and the circuit are open.

Figure 41 also shows the schematic symbols for a knife switch withone set of contacts, single-pole double-throw (SPDT) and the schematicsymbol for a double-pole double-throw (DPDT) knife switch. Dontworry about what a pole or a throw is, you will learn this later.


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OPERATOR

CONTACTS

KNIFE SWITCH

SPDTSWITCH

DPDTSWITCH

SCHEMATICSYMBOL

Figure 41. A Knife Switch and its Schematic Symbols

Pushbutton SwitchA pushbutton switch consists of a pushbutton-type operator and one

or more sets of contacts, as shown in figure 42. Pushing the operatorcauses the contacts to be opened or closed depending on the normalstate. Most pushbuttons have a set of normally open (N.O.) contacts anda set of normally closed (N.C.) contacts.

Figure 43 shows the schematic symbol of a normally openpushbutton switch and a normally closed pushbutton switch.


1PB

1PB

NORMALLY OPEN CONTACTS NORMALLY CLOSED CONTACTS

Figure 43. Schematic Symbols for a Pushbutton Switch

Figure 42. The Construction of a Pushbutton Switch

NORMALLY OPENCONTACTS

NORMALLY CLOSEDCONTACTS

PUSHBUTTONOPERATOR

Selector SwitchA selector switch is much like a pushbutton in its design, as shown

in figure 44. However, instead of pushing a button, you rotate a knob. Aselector switch knob may be designed to stay in a selected position ormay have a momentary action like the pushbutton switch.

Figure 45 shows the symbols for a selector switch with normallyopen contacts and normally closed contacts.




Figure 45. Schematic Symbols for a Selector Switch

Figure 44. The Construction of a Selector Switch



OPERATOR

SKILL 3 CONNECT AND OPERATE A CIRCUIT USING THREE TYPESOF MANUAL SWITCHES

q 1. Position yourself in front of the T7017.q 2. Perform the following substeps 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.q 3. Connect the circuit shown in figure 46.

Figure 47 shows how to connect the wires to the terminals. Notice in figure 46 the schematic symbol of a lamp.


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Procedure OverviewIn this procedure, you will connect three types of

manual switches in an electrical circuit and use them tocontrol a lamp.

SOURCE SELECT

AC DC

12V 12V24V

SWITCHMODULE

LAMPMODULE

12V

+

SCHEMATIC

+-

Figure 46. A Circuit with a Knife Switch and a Lamp

q 4. Perform the following substeps to operate the circuit.A. Turn on the main power switch.B. Close the knife switch and observe the lamps status.

Lamp status _________________________________ (On/Off)The lamp should be on (lighted).

C. Open the knife switch and observe the lamps status. Lamp status __________________________________(On/Off)The lamp should be off.

D. Repeat closing and opening the switch a few more times tobecome more familiar with its operation.A knife switch is a very basic manually-operated switch. Themain power disconnect switch on a residential or commercialelectrical 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. Itis basically the same as having two separate switches in one.This switch has two switches with a N.O. contact, a common(C) contact, and a N.C. contact. If you want the normally openstate, you would connect to a N.O. contact and a commoncontact. If you want the normally closed state, you wouldconnect to a N.C. contact and the common contact.

q 5. Now close the knife switch in the other direction and observe thestatus 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 contactsand they do not affect the lamp.


TERMINALPOST

SPADECONNECTOR

WIRE

INSERT

SCREW DOWNTO SECURE

SPADECONNECTOR

WIRE

CONNECTION

Figure 47. How to Connect the Wires to the Terminals on the ModelT7017 Electrical System

q 6. Turn off the main power switch.All indicator lights should go out.

q 7. Disconnect all wires from the components and the power supplyterminals.

q 8. Connect the circuit represented by the schematic diagram in figure 48.

q 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 timesto familiarize yourself with its operation.

q10. Turn off the main power switch.q11. Disconnect the wires connected to the components and the power

supply output terminals.


12V

PUSHBUTTONSWITCH

+

SCHEMATIC

LAMP

SOURCE SELECT

AC DC

12V 12V24V

LAMPMODULE

-

+

PUSHBUTTONSWITCHMODULE

Figure 48. A Schematic Diagram and Pictorial of a Circuit with a Pushbutton Switch and a Lamp

q12. Connect the circuit represented by the schematic diagram in figure 49.

q13. 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 fewmore times to familiarize yourself with its operation.Another type of selector switch is the one on the front panel ofyour training unit. This switch is used to turn the main poweron and off. Another just like it is used to select between AC orDC output. These are instrument-quality selector switches.They have a different appearance but operate the same as theirindustrial counterparts.

q14. Perform the following substeps to turn off and secure the powersupply.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.


SOURCE SELECT

AC DC

12V 12V24V

LAMPMODULE

12V

+

SELECTORSWITCH

SELECTORSWITCHMODULE

LAMP

SCHEMATIC

-

+

Figure 49. Schematic Diagram and Pictorial of a Circuit with a Selector Switch and a Lamp



hT ir sewsnA1. A simple method for opening and closing a circuit is to use a

__________.

2. The two main components of a switch are the __________and the contacts.

3. The two basic categories of electrical switches are manualand _________.

4. There are _________ types of operators used on manualswitches.

5. A _________ makes a manually-operated switchmomentary.

SEGMENT 4

OUTPUT DEVICES

OBJECTIVE 11 DESCRIBE THE FUNCTION OF FIVE TYPES OF ELECTRICALOUTPUT DEVICES AND GIVE AN APPLICATION OF EACH

There are many types of electrical output devices that can be used inan electrical circuit. We are going to consider five types:

Lamp - A lamp or indicator light gives off light when electricalcurrent flows through its resistive (usually wire) element. They are used on many pieces of equipment to indicate a certain state ofoperation. They can indicate when the power is on, that a certainaction is being performed, or can alert you to a possible danger orproblem.

Resistor - A resistor limits the flow of electrical current. It is oneof the most commonly used components in an electrical circuit.Resistors are often used with motors to suppress the surge ofcurrent and allow the current to the motor to be graduallyincreased. Many electronic devices use resistors as internalcomponents to control voltages and current.


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Buzzer - A buzzer is a type of output device that produces sound. Buzzers are used in doorbells and alarm systems.

Solenoid - A solenoid produces linear mechanical motion fromelectrical energy. Solenoids are used to operate flippers in pinballmachines, operate fluid power valves and turn motors on and off.

Motor - A motor is the output device that produces rotarymechanical motion. You see many examples of motors each day.A fan, for example, uses a motor to turn the blades.


Figure 50. Output Devices

LAMP

MOTOR

BUZZER

RESISTOR

SOLENOID

OBJECTIVE 12 DESCRIBE THE OPERATION OF FIVE TYPES OF ELECTRICALOUTPUT DEVICES AND GIVE THEIR SCHEMATIC SYMBOLS

The schematic symbols for the five output devices just discussed areshown in figure 52, along with a picture of each device. The operation of each is described as follows:

Lamp - A lamp contains a resistive element inside a glass bulb.The bulb is filled with a gas. When current flows through theelement, the element heats up and excites the gas. This producesthe light that we see.

Resistor - A resistor is made of a material that does not allowcurrent to easily flow through it. The most common material usedto make resistors is carbon. Resistors come in a wide range ofvalues.

Buzzer - When electricity is applied to a buzzer, it causes avibration to occur inside the buzzers housing. This vibration is whatcauses the buzzing noise.

Solenoid - The solenoid has an armature or plunger that moves in a linear motion when electrical current is applied to its electricalcoil, as shown in figure 51.

Motor - When electricity is applied to a motor, a magnetic fieldis set up inside it. This magnetic field causes a shaft inside themotor to start rotating. Whatever is attached to the shaft alsorotates.


ARMATURE(PLUNGER)

WIRE COIL

"C" FRAME

MAGNETICFLUX

PLUNGERMOVEMENT

SOLENOID DEENERGIZED SOLENOID ENERGIZED

Figure 51. Construction and Operation of a Solenoid

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Figure 52. Output Devices and their Schematic Symbols

ELECTRIC OUTPUT DEVICES

DEVICE SCHEMATIC SYMBOL

LAMP

RESISTOR

BUZZER

SOLENOID

MOTOR

MM

SKILL 4 CONNECT AND OPERATE AN ELECTRICAL CIRCUITWITH A RESISTOR

q 1. Perform the following substeps to connect the power supply.A. Make sure the main power switch is OFF.B. Place the AC-DC selector switch in the DC position.C. Make sure there are no wires connected to the power supply

terminals. q 2. Connect the circuit shown in the schematic diagram in figure 53.


Procedure OverviewIn this procedure, you will connect a resistor in an

electrical circuit and use a pushbutton switch to control the current flow to it. You should also note that when current is applied to the resistor, the resistor body becomes hot.

SOURCE SELECT

AC DC

12V 12V24V

12V

+

SELECTORSWITCH


OHM MODULE

RESISTOR

25 RESISTOR

25

-

+

SCHEMATIC

Figure 53. A Schematic Diagram and Pictorial of a Circuit with a Pushbutton Switch and a Resistor

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q 3. Perform the following substeps to operate the circuit.A. Turn on the main power switch.B. Face the operator of the selector switch and make sure it is

turned to the left-hand position. This position will put thecontacts in their normal state (open).

C. Change the position of the selector switch selector knob to theright-hand position. This will cause the contacts to close.

D. Put your hand close to the resistor body.

Resistor status______________________________ (Hot/Cool)It should get hot.When electrical current flows through a resistor it gives offheat. For most circuits, this heat is carried away by a fan orsome type of cooling system. However, this concept can beapplied for applications where heat is the desired output.The heating elements used on electric ranges or electric hotwater heaters are basically resistors.

E. Return the selector switch to the left-hand position and waitabout 30 seconds. Then check the resistor again.Resistor status______________________________ (Hot/Cool)The resistor body should be cool.

F. Repeat energizing the selector switch and feeling the resistorbody to familiarize yourself with the operation.

q 4. Perform the following substeps to turn off and secure the powersupply.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.


CAUTIONDo not physically touch the resistor body. It gets very hot and

can burn you.CAUTION

noituaC

NOTEThis is the same basic operation as turning on and off a

heater.

hT i secitoN

SKILL 5 CONNECT AND OPERATE AN ELECTRICAL CIRCUITWITH A BUZZER


terminals.q 2. Connect the circuit shown in the schematic diagram in figure 54.

Be sure to observe the polarity of the buzzer when you connect it.


SOURCE SELECT

AC DC

12V 12V24V

BUZZERMODULE

12V

+

PUSHBUTTONSWITCH


BUZZER

-+

-

+

-+

SCHEMATIC

Figure 54. A Schematic Diagram and Pictorial of a Circuit with a Pushbutton Switch and a Buzzer

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Procedure OverviewIn this procedure, you will connect a buzzer in an

electrical circuit and use a pushbutton switch to control it.

q 3. Perform the following substeps to operate the circuit.A. Turn on the main power switch.B. Press and hold the pushbutton switch and listen.

Buzzer status___________________ (Sounding/Not Sounding) The buzzer should sound.

C. Release the pushbutton switch and listen.Buzzer status___________________ (Sounding/Not Sounding)The buzzer should stop.This is like pushing a doorbell button.

D. Repeat pressing and releasing the pushbutton switch a fewmore times.

q 4. Perform the following substeps to turn off and secure the powersupply.A. Turn off the main power switch.B. Disconnect any wires and components that may be connected

to the power supply output terminals and store them.


SKILL 6 CONNECT AND OPERATE AN ELECTRICAL CIRCUITWITH A SOLENOID


terminals. q 2. Connect the circuit shown in the schematic diagram in figure 55.

q 3. Perform the following substeps to operate the circuit.A. Turn on the main power switch.B. Insert the armature of the solenoid barely into the solenoid.C. Push and hold the pushbutton switch and observe the armature.

Armature status _______________________________(In/Out)The armature should be pulled inside the solenoid or retracted.

D. Release the pushbutton switch and pull the armature out.E. Repeat steps C and D a few more times.


SOURCE SELECT

AC DC

12V 12V24V

SOLENOIDMODULE

12V

+

PUSHBUTTONSWITCH


SOLENOID

-

+

SCHEMATIC

Figure 55. A Schematic Diagram and Pictorial of a Circuit with a Pushbutton Switch and a Solenoid

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Procedure OverviewIn this procedure, you will connect a solenoid in an

electrical circuit and control it using a pushbutton switch.

q 4. Perform the following substeps to turn off and secure the powersupply.A. Turn off the main power switch. B. Disconnect any wires and components that may be connected


SKILL 7 CONNECT AND OPERATE AN ELECTRICAL CIRCUITWITH A MOTOR


terminals.q 2. Connect the circuit shown in the schematic diagram in figure 56. Be

sure to observe the polarity of the fan motor when you connect it.


SOURCE SELECT

AC DC

12V 12V24V

FANMODULE

12V

+

SELECTORSWITCH


M+ -

SCHEMATIC

-

-

+

+

Figure 56. A Schematic Diagram and Pictorial of a Circuit with a Selector Switch and a Motor

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Procedure OverviewIn this procedure, you will connect and operate the

motor of a fan and use a selector switch to control it.

q 3. Perform the following substeps to operate the circuit.A. Make sure the selector knob is to the left and turn on the main

power switch.B. Rotate the selector switch in the circuit and observe the fan.

Fan status _______________________ (Blowing/Not Blowing)The fan should start blowing.

C. Rotate the selector switch back to the left and observe the fan.Fan status _______________________ (Blowing/Not Blowing)The fan should stop blowing.This is basically how your fan at home works.

D. Repeat energizing and releasing the selector switch a few moretimes to familiarize yourself with the operation.

q 4. Perform the following substeps to turn off and secure the powersupply.A. Turn off the main power switch.B. Unplug the main power cord from the wall outlet.C. Disconnect any wires and components that may be connected





hT ir sewsnA1. A _________ is an output device that gives off light.

2. A _________ produces mechanical linear motion.

3. A resistor will give off ______________.

4. A buzzer would give off ____________.

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