AC/DC
ELECTRICAL
SYSTEMS
LEARNING
ACTIVITY
PACKET
ELECTRICAL
MEASUREMENTS
BB227-BC02UEN
LEARNING ACTIVITY PACKET 2
ELECTRICAL MEASUREMENTS
INTRODUCTION
This LAP will discuss how to perform basic measurements of voltage, resistance, and
current in series and parallel circuits. The skills will be used every time to troubleshoot or
test an electrical circuit.
ITEMS NEEDED
Amatrol Supplied
1
T7017 AC/DC Electrical Learning System
FIRST EDITION, LAP 2, REV. B
Amatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registered trademarks of Amatrol,
Inc. All other brand and product names are trademarks or registered trademarks of their respective companies.
Copyright © 2012 by AMATROL, INC.
All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by any means, 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., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584 www.amatrol.com
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TABLE OF CONTENTS
SEGMENT
1 VOLTAGE MEASUREMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
OBJECTIVE
OBJECTIVE
OBJECTIVE
SKILL
OBJECTIVE
1
2
3
1
4
SEGMENT
2 INTRODUCTION TO SERIES AND PARALLEL CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Define voltage and give its units of measurement
Describe the function of two types of voltmeters and give their schematic symbol
Describe how to use a voltmeter to measure voltage
Use an analog voltmeter to measure the voltage at a point referenced to ground
Describe the function of two multimeters: analog and digital
Activity 1 Identification of digital multimeter components
SKILL 2 Use a DMM to measure the voltage of a point referenced to ground
OBJECTIVE 5 Define series and parallel circuits
OBJECTIVE 6 Describe the voltage characteristics in series and parallel circuits
Activity 2 Voltage characteristics of series and parallel circuits
SKILL 3 Use a DMM to measure voltage drops in series and parallel circuits
SEGMENT
3 CURRENT MEASUREMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
OBJECTIVE 7
OBJECTIVE 8
OBJECTIVE 9
SKILL 4
SKILL 5
OBJECTIVE 10
SEGMENT
Define current and give its units of measurement
Describe the function of two types of ammeters and give their schematic symbol
Describe how to use an ammeter to measure current
Use a DMM to measure the electrical current
Use a DMM to measure current in series and parallel circuits
Describe the current characteristics in series and parallel circuits
Activity 3 Characteristics in series and parallel circuits
4 RESISTANCE MEASUREMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
OBJECTIVE 11
OBJECTIVE 12
OBJECTIVE 13
SKILL 6
OBJECTIVE 14
SKILL 7
OBJECTIVE 15
SKILL 8
Define resistance and give its units of measurement
Describe the function of two types of ohmmeters and give their schematic symbol
Describe how to use an ohmmeter to measure resistance
Use a DMM to measure the resistance of a component
Describe the resistance characteristics in series and parallel circuits
Measure the resistance in series and parallel circuits
Describe two methods of measuring continuity
Test the continuity of wires using a DMM
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SEGMENT 1
VOLTAGE MEASUREMENT
OBJECTIVE 1
DEFINE VOLTAGE AND GIVE ITS UNITS OF MEASUREMENT
In order for anything to move, a force must be applied to it that is greater in
one direction than another.
For example, if forces A and B (figure 1) are equal the object will not move. If
force A is greater than force B the object will move to the right. If force A is less
than force B the object will move to the left. In other words, what causes the object
to move is not the value of the forces on it, but the difference between them.
FORCE
ORCE B
OBJECT
Figure 1. Opposing Forces
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We call the force that causes electrons to move (flow) in an electrical circuit
voltage. In fact, another name for voltage is electromotive force. As with any force,
this voltage value is measured as a difference in potential (force) between two
points.
BATTERY
+
CONVENTIONAL
CURRENT
FLOW
RESISTOR
HIGH
POTENTIAL
POTENTIAL
DIFFERENCE
(VOLTAGE)
LOW
POTENTIAL
Figure 2. Potential Difference
The basic unit used to measure the voltage (potential difference) in a circuit is
the volt. The abbreviation for a volt is V. You would represent 20 volts as 20V, 5
volts as 5V, etc.
You can expand this abbreviation to include how the electromotive forces
(voltage) cause electrons to flow. Current can be either direct or alternating directions. We call direct current flow DC, so in our examples 20 volts would be 20VDC,
5 volts 5VDC, etc. If the current is alternating current or AC, write it as 240VAC,
5VAC. When only the V is used, it is understood to be DC.
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OBJECTIVE 2
DESCRIBE THE FUNCTION OF TWO TYPES OF VOLTMETERS AND
GIVE THEIR SCHEMATIC SYMBOL
A voltmeter is a device that measures the voltage between two points in an
electrical circuit. The value of this voltage is displayed on an analog display or on
a digital display, as shown in figure 3.
DIGITAL DISPLAY
ANALOG DISPLAY
5
10
15
20
0
25
30
A-C VOLTS
Figure 3.
Analog and Digital Voltmeters
The voltmeter is a key tool for troubleshooting and analysis of circuits. In
some cases, schematic diagrams may even specify a voltmeter as part of the circuit.
Figure 4 shows the electrical schematic symbol for a voltmeter.
V
Figure 4. The Voltmeter Schematic Symbol
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OBJECTIVE 3
DESCRIBE HOW TO USE A VOLTMETER TO MEASURE VOLTAGE
Two points are needed to measure voltage because voltage is the difference
between the potential of two points in an electrical circuit. The value measured
depends on what two points you use. In the circuit shown in figure 5, a power
supply provides a source of both high and low potential. The difference in potential
(voltage) from one side of the power supply to the other is the force that causes
current to flow. In this circuit:
• Point A is the point of highest potential because it is closest to the high
potential terminal of the power supply.
• Point C is the point of lowest potential because it is closest to the low potential side of the power supply.
• Point B is somewhere between A and C in potential because it is separated
by a resistor on each side.
HIGH POTENTIAL
SIDE
+
-
LOW POTENTIAL
SIDE
POWER
SOURCE
A
B
C
POINT OF
HIGHEST
POTENTIAL
THIS POINT IS
AT A VOLTAGE
POTENTIAL THAT
IS BETWEEN THE
HIGH AND LOW
POINT OF
LOWEST
POTENTIAL
Figure 5. Different Points Have Different Potentials
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The actual voltage measured at any point depends on what other point you use
as a reference. To see how this works let’s examine the voltage value at point A
using the two most common ways to measure voltage, as shown in figure 6.
If you measure from point A to point C, you will get a higher value than
measuring from point A to point B because point A is farther from C than B in
potential.
+
-
POWER
SOURCE
A
B
C
SMALLER VALUE
POINT B AS
REFERENCE
LARGER VALUE
POINT C AS
REFERENCE
Figure 6. Measuring Potential of Point A with Reference to Points B and C
You can see how the point of reference is important when measuring voltage.
Most voltage comparisons will use one of these two methods.
1. Compare the point to a common reference of known value (e.g. A to
C).
2. Measure the voltage across the component(s). (e.g. A to B)
In application, a known reference point is called a ground. Grounds are usually
a point connected to the power supply (such as point C above).
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To measure the voltage between two points you must place the voltmeter test
leads as shown in figure 7. The lead that is attached to the positive terminal of the
voltmeter should be attached to the point with the higher (+) potential. The lead
that is attached to the negative terminal of the voltmeter should be attached to the
point with the lower (-) potential.
In the example shown in figure 7, the voltmeter is measuring the voltage at the
point between resistors R1 and R2 referenced to the ground of the power supply,
which is the negative terminal.
LOWER
POTENTIAL
+
5
10
15
20
0
25
30
A-C VOLTS
R1
R2
R3
HIGHER
POTENTIAL
VOLTMETER
POSITIVE
LEAD
Figure 7.
+
NEGATIVE
LEAD
Proper Placement of the Test Leads to Measure Voltage
Most voltmeters have range switches that allow you to select the voltage range
that you wish to measure. All voltage measurements should be measured from the
lowest voltage range possible. However, it is good practice to measure from the
highest voltage range setting first. Voltage measurements starting using the highest
voltage range allows you to switch to lower voltage range values to get a more
accurate voltage reading. This also helps to protect analog meters from damage.
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SKILL 1
USE AN ANALOG VOLTMETER TO MEASURE THE VOLTAGE AT A
POINT REFERENCED TO GROUND
Procedure Overview
In this procedure, you will use an analog voltmeter to measure AC and
DC voltages. First, you will measure the output voltages available from the
T7017 power supply. Then you will connect a circuit and measure the voltage
at different points in the circuit referenced to ground.
Although the scale indicates AC volts, the meter will actually measure AC
or DC volts.


1. Locate the voltmeter on the T7017.
This voltmeter is an analog voltmeter because the display uses an analog
scale, as you can see in figure 8.
5
10
15
20
25
30
0
A-C VOLTS
Figure 8. An Analog Voltmeter Scale

The scale on this voltmeter ranges from 0 volts to 30 volts. The indicator
moves across the scale when voltage is applied through the test leads. Each
tick mark on the scale represents 1/2 volt. For example, the voltage indicator
in figure 8 indicates 8.5 volts.
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
2. Perform the following substeps to prepare the T7017 for use.
A. Make sure the main power switch is off.
B. Plug the power cord into an available wall outlet.
C. Make sure there are no wires connected to the power supply output
terminals.

3. Perform the following substeps to prepare the analog voltmeter, as shown in
figure 9.
A. Locate two test leads.
B. Plug one test lead into the positive (red) terminal of the voltmeter, located
just under the voltmeter scale as shown in figure 9.
NEGATIVE LEAD
POSITIVE LEAD
SCHEMATIC
+
CENTER
TERMINAL
12V
+
V
VOLTMETER
Figure 9. Measuring the 12 Volt Supply
NOTE
The color red is associated with a positive connection on a circuit while
black is associated with a negative or ground.
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C. Plug the other test lead into the negative (black) terminal of the voltmeter.
NOTE
Colored wires are used for helping you quickly identify positive and
negative connections. Any wire will work in an electrical circuit regardless of
color.
D. Insert the test lead that is connected to the positive terminal of the voltmeter into the right terminal of the power supply, as shown in figure 10.
This is the positive (+) terminal of the power supply.
E. Insert the test lead that is connected to the negative terminal of the voltmeter into the center terminal of the power supply, as shown in figure 10.
The center output terminal on the power supply is the ground..

4. Perform the following substeps to measure the DC output voltage of the
power supply.
A. Turn the AC-DC selector switch to DC.
MAIN POWER
SWITCH
AC/DC SELECTOR
SWITCH
MODEL 7017
Figure 10. Front Panel of the T7017
B. Make sure the circuit breaker is in the on (right) position.
C. Turn on the power supply.
D. Record the voltmeter reading.
DC Voltmeter reading __________________________________ (VDC)
It should indicate approximately 12 volts.

5. Turn the AC-DC selector switch to AC.

6. Repeat step 5 to measure the AC output voltage.
AC Voltmeter reading _____________________________________ (VAC)


The reading should be fairly close to the DC voltage reading. However, this
reading is in AC.
7. Turn off the main power switch.
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
8. Remove the test leads from the power supply terminals.

9. Turn the AC/DC selector switch to DC.


10. Connect the circuit shown in figure 11.
This circuit has two loads so there will be more than two voltage points to
measure.
SOURCE SELECT
AC
DC
24V
12V
12V
10 RESISTOR
OHM MODULE
25 RESISTOR
OHM MODULE
SCHEMATIC
+12V
R1 = 10
R2 = 25
Figure 11. Circuit with Two Resistors
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MODEL 7017
SOURCE SELECT
5
10
15
20
0
25
30
A-C VOLTS
AC
DC
24V
12V
12V
VOLTMETER
-
R1
POINT
1
+
GROUND
TERMINAL
TEST
LEAD
R2
POINT
3
POINT
2
POSITIVE
TERMINAL
TEST
LEAD
POINT
4
SCHEMATIC
GROUND
+12V
V
+
R1 = 10
POINT
1
POINT
2
VOLTMETER
R2 = 25
POINT
3
POINT
4
Figure 12. Voltage of Point 1 Measured Referenced to Ground

11. Turn on the main power switch.

12. Connect the voltmeter test leads, as shown in figure 12, to test the voltage of
point 1 referenced to ground.
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
13. Read the voltmeter scale.
Point 1 Voltage __________________________________________ (VDC)

The voltage at point 1 referenced to ground should be approximately 12
VDC. This is the output voltage of the power supply. The voltage here is the
same as at the output terminal of the power supply because the current at this
point in the circuit has not yet passed through any of the loads in the circuit.

As the current flows through each component, the components uses up a
certain amount of the applied voltage. The voltage that is used by each load
is called a voltage drop. The amount of this drop is directly related to the
resistance of the load. You will learn more about this later.

14. Turn off the main power switch.

15. Move the test lead that is connected to the positive terminal of the voltmeter
to Point 2, as shown in figure 12.

16. Turn on the main power switch and read the voltmeter scale.
Point 2 Voltage __________________________________________ (VDC)


The voltage of point 2 referenced to ground should be approximately 8.5
volts. This shows that some of the voltage was used by the resistor 1.
17. Repeat steps 15 and 16 to measure the voltage referenced to ground at points
3 and 4.
Point 3 Voltage __________________________________________ (VDC)
Point 4 Voltage __________________________________________ (VDC)

The voltage of point 3 is the same as at point 2 because these two points are
connected by a wire, which has practically no resistance.

The voltage at point 4 is 0 V. This shows that the remainder of the voltage was
used by resistor 2. The voltage at point 4 and ground are the same because
they are connected by a wire with almost no resistance. Remember that the
voltmeter measures the difference in voltage between two points.

18. Turn off the main power switch.

19. Remove the test leads from the circuit.

20. Disconnect the test leads from the voltmeter terminals and store them.

21 Disconnect the circuit and store all components.
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OBJECTIVE 4
DESCRIBE THE FUNCTION OF TWO MULTIMETERS:
ANALOG AND DIGITAL
A multimeter is a multi-purpose device that can measure voltage, current and
resistance. Multimeters are available with either an analog display or a digital
display.
Analog multimeters, like the one in figure 13, are used when there are very
fast changes in a reading because the needle responds faster than a digital readout.
Figure 13. An Analog VOM
A multimeter with a digital display is called a digital multimeter (DMM).
The measurement readings of a DMM are much easier to read because they are
displayed in digital form, much like the readout on your calculator. Figure 14
shows a typical DMM.
Figure 14. A Digital Multimeter (DMM)
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Activity 1. Identification of Digital Multimeter Components
Procedure Overview
In this procedure, you will identify and learn the functions of the basic
components of the digital multimeter supplied with your T7017.

1. Locate the DMM supplied with your T7017, as shown in figure 15.
Figure 15. Digital Multimeter


2. Locate the Function/Range Switch of the model Wavetek Model DM30XR
DMM, as shown in figure 16.
This is a 30-position rotary selector switch that performs three functions:
•Turns
the DMM power on/off
•Selects
the type of measurement (AC/DC voltage, AC/DC current, resistance and continuity)
•Selects
the measurement range
NOTE
When measuring an unknown quantity, always start with the highest range
setting. You can then decrease the range setting until you get an accurate
reading.
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The switch face is divided into five sections that are labeled in figure 16.
Positioning the rotary switch to one of these sections determines the type
of measurement to be taken. The numbers within each section tell you the
maximum value which may be measured in that position.

DIGITAL
DISPLAY
MINIMUM/MAXIMUM
BUTTON
30XR
NON-CONTACT
VOLTAGE BUTTON
NON-CONTACT
VOLTAGE INDICATOR
LIGHT
NON
CONTACT
VOLTAGE
MIN MAX
AC VOLTAGE
SECTION
HOLD
DATA HOLD
BUTTON
V
200
600 OFF 600
200
20
V
20
2
200m
CONTINUITY
SELECTION
2
200m
200
20M
2m
2M
20m
200k
200m
20k
2k
200
RESISTANCE
SECTION
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
10A
CAT
CAT
V
COM
BATTERY
VOLTAGE
SELECTION
DC VOLTAGE
SECTION
A
600V
300V
BATT 9V
DC CURRENT
SECTION
200mA
MAX
FUSED
10A MAX
FUSED
FUNCTION/RANGE
SWITCH
MAX
600V
600V
AC CURRENT
SECTION
TEST LEAD
TERMINALS
Figure 16. Wavetech Meterman 30XR Controls and Display


3. Locate the DC Voltage section, as shown in figure 16.
Turning the function/range selector switch to this section sets the meter
to measure DC voltage. The numbers along the selector knob indicate DC
voltage values.
NOTE
The maximum value of DC voltage that can be measured is 600 VDC.
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
4. Locate the DC Current section, as shown in figure 16.

Turning the function/range selector switch to this section sets the meter to
measure DC current. The numbers along the selector knob in this section
indicate current values.

The range that you select in this section can also affect the placement of the
test leads.
NOTE
The maximum value of DC current that can be measured is 10 amps.

5. Locate the AC Current section, as shown in figure 16.

Turning the function/range selector switch to this section sets the meter to
measure AC current. The numbers along the selector knob in this section
indicate current values.

The range that you select in this section can affect the placement of the test
leads, as you will learn later.
NOTE
The maximum value of AC current that can be measured is 10 amps.


6. Locate the Resistance section, as shown in figure 16.
Turning the function/range selector switch to this section sets the meter to
measure resistance. The Greek letter omega () represents resistance. The
numbers along the selector knob in this section indicate resistance values.
You will learn more about resistance measurements later.
NOTE
The maximum resistance value that can be measured with this meter is 20
M (20 mega-ohms or 20,000,000 ohms).


7. Locate the Continuity selection, as shown in figure 16.
Turning the function/range selector switch to this selection sets the meter to
check for continuity. This selection is not associated with any other section.
You will learn more about continuity later.
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
8. Locate the AC Voltage section , as shown in figure 16. The function/range
selector switch sets the meter to measure AC voltage. The numbers along
the selector knob in this section indicate voltage ranges. When you set the
selector knob to one of these numbers, the meter will be able to measure any
value less than the selected value.

If the reading being taken is higher than the selected value, “OL” appears on
the display. The range setting must be increased if this occurs.

If “OL” is displayed while measuring current or voltage with the range set to
its highest value, remove the meter from the circuit. The value is beyond the
capability of this DMM.
NOTE
The maximum value of AC voltage that can be measured is 600 VAC.


9. Locate the Digital Display, as shown in figure 16.
Since the display on the DMM is a digital display, reading the measurement
results is fairly simple. The digital display will give you a digital value, such
as 1.45. The value displayed is read in the units indicated by the position of
the Function/Range switch.
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
10. Locate the Test Lead Terminals, as shown in figure 17.
Figure 17. Test Lead Terminals



There are four terminals. The terminal labeled “COM” is a common
connection point. You will use this terminal when making all measurements.
To measure voltage or resistance, you would use the right terminal “V ” and
the “COM” terminal.
To measure current less than 200 mA (200 milli-amps or 0.2 amps), you would
use the “mA” terminal and the “COM” terminal. To measure current greater
than 200 mA, but less than 10 amps, you would use the “10A” terminal and
the “COM” terminal.
CAUTION
Never attempt to take a voltage reading when the DMM leads are installed
in the current terminals, this will damage the meter. The DMM has a built in
feature that sounds a warning buzzer when the lead location and the Function/
Range switch settings will result in damage to the DMM.


11. Locate the Battery voltage selection.
The battery voltage selection allows you to easily measure the voltage of 1.5
volt and 9 volt batteries. A good 1.5 volt battery will measure a value greater
than 1.2 volts. A good 9 volt battery will measure a value greater than 7.2
volts.
NOTE
You will not use the meter components described in steps 11 - 14 in
the Electrical Systems Learning System curriculum. However, it is good to
understand their functions.
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





12. Locate the Minimum/Maximum button, as shown in figure 16.
This function allows you to capture and display the minimum or maximum
reading associated with a selected mode of measurement.
13. Locate the Data Hold button, as shown in figure 16.
This pushbutton switch keeps data on the display even after you remove the
test leads from the component being measured.
14. Locate the Non-contact voltage button and non-contact voltage indicator
light.
This feature allows you to test the presence of voltage in a range of 70-600
volts without physically touching the probes to the circuit. This feature is
nice if you only need to determine if a circuit is “hot” (has voltage).
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SKILL 2
USE A DMM TO MEASURE THE VOLTAGE OF A POINT
REFERENCED TO GROUND
Procedure Overview
In this procedure, you will make both AC and DC voltage measurements
using a DMM.

1. Perform the following substeps to measure DC voltage.
A. Turn the Function/Range Switch to the OFF position.
B. Plug the red test lead in the right (V) terminal.
C. Plug the black test lead into the terminal labeled COM.
D. Rotate the Function/Range switch to the 600 position in the DC Voltage
section.

2. Connect the circuit shown in figure 18.
SCHEMATIC
SOURCE SELECT
AC
+12V
+
DC
-
24V
12V
12V
R1 = 10
POINT
1
POINT
1
10
RESISTOR
OHM
MODULE
POINT
2
25
RESISTOR
OHM
MODULE
R2 = 25
POINT
2
POINT
3
POINT
3
Figure 18. Two Resistor Circuit

3. Turn on the T7017 power supply.
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
4. Place the AC-DC selector switch on the T7017 power supply in the DC
position.

Measuring voltage in circuit with the DMM is similar to an analog voltmeter.
To measure the DC voltage between two points you connect the red lead
from the positive terminal of the DMM to the point with the higher potential.
The black lead from the negative (common) terminal of the DMM is then
connected to the point with the lower potential.

If your leads are reversed when you measure DC voltage, it will not harm the
DMM. The voltage value will be displayed with a minus (-) sign.

5. Perform the following substeps to measure the voltage at points 1, 2, and 3
with reference to ground.
A. Place the red test lead of the DMM on point 1 as indicated in figure 18.
B. Place the black test lead of the DMM in the ground (center) terminal of
the T7017 power supply.
C. Record the voltage reading of point 1 referenced to ground in figure 19.
Point 1 Voltage = _______________________________________ VDC
It should be approximately +012 volts. Notice that a 0 appears in front of
the 12. This means that the meter can provide a more accurate reading at
a lower voltage range setting.
600 VOLT
POSITION
(VDC)
Point 1
200 VOLT
POSITION
(VDC)
20 VOLT
POSITION
(VDC)
2 VOLT
POSITION
(VDC)
+012 Volts
Point 2
Point 3
Figure 19. Two Resistor Circuit DC Voltage (VDC) Readings
D. Rotate the Function/Range switch to 200 VDC and record the voltage
reading on the table in figure 19.
It should be approximately +11.6 volts. Notice that the value you recorded
in substep C has changed from 12 to 11.6. This is because the voltage
range setting is closer to the actual voltage of Point 1.
E. Rotate the Function/Range switch to 20 VDC and record the voltage
reading on the table in figure 19.
It should be approximately +11.64 volts. Notice that the value you
recorded in substep D has changed from 11.6 to 11.64. This is because the
voltage range setting is closer to the actual voltage of Point 1.
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F. Rotate the Function/Range switch to 2 VDC and record the voltage reading
on the table in figure 19.
You should notice that the meter displays “OL”. This means that an overload condition exists because the voltage measured is higher than the
voltage range setting on the DMM.
G. Leave the black lead in the ground terminal and move the red test lead to
point 2.
H. Repeat substeps C F to determine the voltage readings for point 2.
I. Leave the black lead in the ground terminal and move the red test lead to
point 3.
J. Repeat substeps C F to determine the voltage readings for point 3.

6. Connect the leads to measure the voltage at point 1 with black lead connected
to point 1 and the red lead connected to ground.

7. Turn the Function/Range switch to 20 VDC and record the voltage reading.
Point 1 voltage __________________________________________ (VDC)

You should notice that the voltage is -11.64 VDC. It is the same as in step 5E
except that there is a minus sign. This tells you that the difference in voltage
between point 1 and ground is 11.64 volts. The negative sign tells you that
ground is 11.64 volts less in potential than point 1.

8. Remove the test leads from the ground terminal and the circuit.

9. Turn the AC/DC selector switch on the T7017 to AC.

10. Set your DMM to the highest AC voltage range.

11. Repeat step 5 to measure the voltage at points 1, 2, and 3 with reference to
ground in the table shown in figure 20.

The values should be approximately the same as the values you recorded in
the previous table.
600 VOLT
POSITION
(VAC)
200 VOLT
POSITION
(VAC)
20 VOLT
POSITION
(VAC)
2 VOLT
POSITION
(VAC)
Point 1
Point 2
Point 3
Figure 20. Two Resistor Circuit Voltage (VAC) Readings
NOTE
If you were to reverse the test leads (red to the ground terminal and black
to the points in the circuit), the DMM would not indicate a polarity change
because AC does not have polarity.
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
12. Remove the test leads from the power supply terminals.

13. Perform the following substeps to turn off and secure the T7017 power
supply.
A. Turn off the main power switch.
B. Make sure to disconnect any wires or components connected to the output
terminals of the power supply.

14. Now perform the following substeps to measure the output voltage of a wall
outlet.
CAUTION
Be careful not to touch the metal probe tips while inserting them into the
outlet.
A. Make sure the DMM is set to measure AC voltage and is set to its highest
range. If you are unsure about these settings, ask your instructor for assistance before you proceed.
B. Insert the red lead into the left slot of the outlet and the black lead into the
right slot, then observe the reading.
Voltage reading _______________________________________ (VAC)
The actual voltage reading depends on your location. Different countries provide different voltages. Ask the instructor to check your voltage
reading to make sure it is correct for your location.
C. Remove the test leads from the outlet.


15. Disconnect the test leads from the DMM terminals and turn off the DMM.
You have now successfully measured the output voltages of the T7017 power
supply and of a wall outlet with the DMM.
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SEGMENT 1
SELF REVIEW
1. __________ is the existence of a potential difference between two
points in a circuit.
2. Voltage is measured in units called _________.
3. ______________is the abbreviation symbol used for voltage in
equations.
4. The measurement readings of a(n) ____________ are much easier to
read than an analog multimeter.
5. The black lead from the negative (common) terminal of the DMM
should be connected to the point with the ________ potential in the
circuit.
6. The three basic units that can be measured using a multimeter are
________, current, and resistance.
7. A(n) ________________ is a common connection point, or a known
reference point, in an electrical circuit.
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SEGMENT 2
INTRODUCTION TO SERIES AND PARALLEL CIRCUITS
OBJECTIVE 5
DEFINE SERIES AND PARALLEL CIRCUITS
All electrical circuits are made up of a combination of two types of circuits:
series and parallel. In order to learn more about electrical systems, you will have
to learn the characteristics of voltage, current, and resistance in these two types of
circuits.
Series Circuits
A series circuit is one in which there is only one path for current to travel, as
shown in figure 21. The total current in a series circuit flows through each component. It starts at the positive terminal of the power supply and flows through one
component after the other and then back to the negative terminal of the power
supply.
CURRENT
FLOW
RESISTOR 1
+
BATTERY
RESISTOR
2
-
RESISTOR 3
Figure 21. A Series Circuit
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Parallel Circuit
A parallel circuit is a type of circuit that has more than one path for current to
flow, as shown in figure 22. The current flows from the positive terminal through
the circuit until it reaches node 1. It then splits with part of the current flowing
through branch A and part of the current flowing through branch B. The two branch
currents then rejoin each other at node 2 and flow back to the power supply’s negative terminal.
MAIN
FLOW
NODE 1
BRANCH A
+
R1
NODE 2
R2
BRANCH B
Figure 22. A Simple Parallel Circuit
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OBJECTIVE 6
DESCRIBE THE VOLTAGE CHARACTERISTICS
IN SERIES AND PARALLEL CIRCUITS
In a series circuit, the total voltage supplied by the power supply is divided
among the loads, as shown in figure 23. Each load in the circuit uses a certain
amount of the voltage as the current travels through it. This leaves less voltage
available for the next load to use.
The voltage drop across any component is the difference in voltage referenced
to ground between the two terminals of the component. For example, the voltage
drop across load 1 is 4 volts because the voltages at its two terminals referenced to
ground are 10 V (VA) and 6 V (VB).
The amount of voltage that is used by each load (its voltage drop) depends on
the resistance of each load, as you will learn later.
VA = 10V
VB = 6V
CURRENT
VOLTAGE DROP 1
=VA -VB
+
VOLTAGE
DROP 2
=VB -VC
VOLTAGE DROP 3
=VC -VD
VD = 0V
VC = 2.5V
Figure 23. Loads in Series
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When a parallel circuit is connected to a constant voltage power supply, as
shown in figure 24, the same amount of voltage is available to each of the branches
of the circuit. In fact, the voltage available to each branch is equal to the source
voltage.
V1 = 10V
V2 = 10V
V3 = 10V
POINT
3
POINT
2
POINT
1
+
R1
R3
R2
POINT
5
POINT
4
V4 = 0V
V5 = 0V
POINT
6
V6 = 0V
Figure 24. Voltages in a Parallel Circuit
As you can see in figure 24, the voltage at points 1,2, and 3 referenced to
ground are equal since they are all actually the same point. The same is true for
points 4, 5, and 6. This means that the voltage drop across each branch in a parallel
circuit is always the same. In this case, the voltage drop is 10 volts.
NOTE
Points 1, 2, and 3 represent one node, and Points 4, 5, and 6 represent
another node.
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Activity 2. Voltage Characteristics of Series and Parallel Circuits
Procedure Overview
In this procedure, you will connect lamps in series and parallel circuits and
observe the effects. This will help to show the different voltage characteristics
between series and parallel circuits.

1. Connect the circuit shown in figure 25.
Notice that the circuit is connected to the 24 volt terminals.

SOURCE SELECT
SCHEMATIC
AC
DC
+
24V
12V
12V
+
-
24V
LAMP 1
LAMP
MODULE
Figure 25. Test Circuit with One Load

2. Place the AC/DC selector switch on the T7017 in the DC position.

3. Turn on the power supply and observe the lamp.
Lamp status ___________________________________________(On/Off)


The lamp should be on because the circuit is complete. It should also be
burning brightly because it is using all of the voltage available since there are
no other loads in the circuit.
4. Turn off the power.
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
5. Add another lamp to the circuit in series as shown in figure 26.
SOURCE SELECT
SCHEMATIC
AC
+
DC
24V
12V
-
12V
+
24V
LAMP 1
LAMP 2
ADD A LAMP
HERE
LAMP
MODULE
LAMP
MODULE
Figure 26. Test Circuit with Two Loads

6. Turn on the power and observe the lamps.
Lamp 1 status __________________________________________(On/Off)
Lamp 2 status __________________________________________(On/Off)

Both lamps should be on, but they should not be as bright as when there was
only one lamp. This is because the available voltage is being split between the
two lamps.

7. Turn off the power.

8. Add another lamp as shown in figure 27.
+
24V
LAMP 1
LAMP 2
LAMP 3
ADD A LAMP
HERE
Figure 27. Test Circuit with Three Loads
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9. Turn on the power and observe the lamps.

Lamp 1 status __________________________________________(On/Off)
Lamp 2 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)
All three lamps should be on, but dimmer than with only two. Now the
available voltage is being split between the three lamps.


10. Turn off the power supply and disconnect the circuit.

11. Now connect the lamps in parallel as shown in figure 28.
SOURCE SELECT
AC
SCHEMATIC
DC
24V
12V
+
-
+
12V
24V
LAMP
MODULE
LAMP
MODULE
LAMP
1
LAMP
2
LAMP
3
LAMP
MODULE
Figure 28. Test Circuit with Loads in Parallel

12. Turn on the power supply and observe the status of the lamps.
Lamp 1 status __________________________________________(On/Off)
Lamp 2 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)

All three lamps should be on at the same brightness.

Each lamp has the same amount of voltage available to it, 24 volts, the source
voltage.

13. Turn off the power supply.

14. Remove two lamps from the circuit.
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
15. Turn on the power supply and observe the status of the lamps.

You should see that the one lamp burns no brighter because the voltage drop
across it is still 24 volts.

Most AC wiring circuits in buildings use parallel circuits because the loads
can then receive the same voltage. This allows all appliances and other
devices to be designed to operate on the same voltage, such as 120 VAC or
220 VAC.

16. Turn off the power supply.

17. Disconnect the circuit and store all components.
SKILL 3
USE A DMM TO MEASURE VOLTAGE DROPS
IN SERIES AND PARALLEL CIRCUITS
Procedure Overview
In this procedure, measure the voltage drop across each component in
series and parallel circuits. This will teach you how to measure a voltage drop
and more about the voltage characteristics of electrical circuits.

1. Connect the series circuit shown in figure 29.
SCHEMATIC
SOURCE SELECT
A
AC
B
DC
24V
12V
12V
R1 =10
+
R2 =25
12V
R3 =25
D
25
RESISTOR
MODULE
R3
25
RESISTOR
MODULE
R2
10
C
RESISTOR
MODULE
R1
Figure 29. Series Test Circuit
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
2. Perform the following substeps to turn on the power supply.
A. Place the AC/DC selector switch in the DC position.
B. Turn on the power supply.

3. Set the DMM to the highest DC voltage setting.

4. Place the test leads across resistor R1, as shown in figure 30. Make sure the
red test lead from the DMM is connected to the side of the resistor connected
to the positive (+) terminal of the power supply.

Measuring the voltage drop between two points is the same as measuring
with reference to ground.
Measured voltage = ______________________________________ (VDC)

It should be approximately be 2 VDC.
V
R1
Figure 30. Measuring Voltage Dropped Across a Resistor

5. Adjust the voltage range on the DMM until you reach the lowest voltage
range that is still above the reading on the meter.

6. Repeat step 4 for resistors R2 and R3.

If the voltage is displayed with a negative sign, reverse the test leads.
R2 Measured voltage = ____________________________________ (VDC)
R3 Measured voltage = ____________________________________ (VDC)

The voltage drops across R2 and R3 should be the same, approximately
5 VDC. This is because their resistance is the same. Also, because their
resistance value is higher than R1, their voltage drop is higher. You will learn
more about this later.

You can also determine voltage drops across components by measuring
a point before and after each component with reference to ground. The
difference between the two voltage readings will be the voltage drop for that
component. Proceed to the next step to do this.
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
7. Perform the following substeps to determine the DC voltage drops in the
circuit in figure 31 by measuring voltages with reference to ground. The
DMM connections to measure the voltage at point A are shown in figure 31
as a guide.
A. Measure the voltage referenced to ground at the two points: before and
after resistor R1. These points are labeled A and B in figure 31.
Point A Voltage (before R1) = ____________________________ (VDC)
Point B Voltage (after R1) = _____________________________ (VDC)
SCHEMATIC
SOURCE SELECT
A
AC
B
DC
24V
12V
12V
R1 =10
V
+
12V
GROUND
VOLT
METER
R2 =25
R3 =25
D
25
RESISTOR 25 RESISTOR 10 RESISTOR
MODULE
MODULE
MODULE
R3
R2
R1
POINT
B
30XR
NON
CONTACT
VOLTAGE
MIN MAX
V
TEST
LEAD
C
POINT
A
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
TEST
LEAD
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
Figure 31. Measurement of Point Voltage Referenced to Ground
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B. Calculate the voltage drop across R1. This is the difference in voltage
between points A and B.
Voltage Drop R1 = _____________________________________ (VDC)
The voltage should be 2 VDC. This should be the same as measured in
step 4.
C. Repeat substeps A and B for R2.
Point B Voltage (Before R2) = ____________________________ (VDC)
Point C Voltage (After R2 = ______________________________ (VDC)
Voltage Drop R2 = _____________________________________ (VDC)
D. Repeat substeps A and B for R3.
Point C Voltage (Before R3) = ____________________________ (VDC)
Point D Voltage (After R3) = _____________________________ (VDC)
Voltage Drop R3 = _____________________________________ (VDC)
NOTE
If there is only one load in a circuit, the voltage dropped across it should
always equal the source voltage.

8. Turn off the power supply.

9. Prepare the DMM to measure AC volts.

10. Place the AC/DC selector switch in the AC position.

11. Turn on the power supply.

12. Repeat step 4 to measure the AC voltage drop across resistor R1.
R1 Measured Voltage Drop = _______________________________ (VAC)

13. Repeat step 7A to measure the AC voltage at points A and B with respect to
ground. Then calculate the voltage drop as you did in step 7B.
Point A Voltage = ________________________________________ (VAC)
Point B Voltage = ________________________________________ (VAC)
Voltage Drop R1 _________________________________________ (VAC)

The values may be slightly higher than those obtained in steps 4 and 6. The
reason for this is discussed in the AC lessons. However, you can see that AC
and DC voltages react the same in a series circuit with resistors.
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
14. Repeat steps 7C and 7D for R2 and R3.
Point B Voltage _________________________________________ (VAC)
Point C Voltage _________________________________________ (VAC)
Voltage Drop R2 _________________________________________ (VAC)
Point C Voltage _________________________________________ (VAC)
Point D Voltage _________________________________________ (VAC)
Voltage Drop R3 _________________________________________ (VAC)

15. Turn off the power supply.

16. Disconnect the circuit.
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
17. Connect the parallel circuit shown in figure 32.

In the next few steps, you will test the voltage drop characteristics of parallel
circuits.

Notice that the schematic in figure 32 shows the nodes a little differently than
how they are actually connected in the pictorial.
SOURCE SELECT
AC
PUT LEADS
HERE TO
MEASURE
VOLTAGE
ACROSS
THIS
COMPONENT
DC
24V
12V
12V
NODE 1
10 RESISTOR
OHM MODULE
25 RESISTOR
OHM MODULE
NODE 2
25 RESISTOR
OHM MODULE
SCHEMATIC
NODE 1
+
R1 = 10
R2 = 25
R3 = 25
12V
NODE 2
Figure 32. Parallel Circuit
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
18. Place the AC/DC selector switch in the DC position and turn on the power
supply.

19. Prepare the DMM to measure DC volts.

20. Measure the voltage drop across each branch of the circuit.

You can do this by measuring the voltage across the terminals of each
component. For example, the voltage drop across branch 1 is the voltage
drop across resistor R1, as shown in figure 33.
Branch 1 Voltage Drop (R1) = ______________________________ (VDC)
Branch 2 Voltage Drop (R2) = ______________________________ (VDC)
Branch 3 Voltage Drop (R3) = ______________________________ (VDC)
BRANCH
1
BRANCH
2
BRANCH
3
R1
R2
R3
+
12V
V
Figure 33. Measurement of Branch 1 Voltage Drop

You should notice that the voltage drop across each branch is the same. This
is true of parallel circuits. In this case, the voltage drop is the same as the
source voltage, which is approximately 12 VDC.

21. Turn off the power supply.

22. Now switch the power supply to AC.

23. Turn on the power supply.

24. Set the DMM to measure AC volts and repeat step 20.
Branch 1 Voltage Drop (R1) = ______________________________ (VAC)
Branch 2 Voltage Drop (R2) = ______________________________ (VAC)
Branch 3 Voltage Drop (R3) = ______________________________ (VAC)

The voltage should be approximately 12 VAC. Again, AC and DC voltages
act the same in a parallel resistance circuit.

25. Turn off the power supply, disconnect all wires and store all components.

26. Turn off the DMM.
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SEGMENT 2
SELF REVIEW
1. There is only one path for current to travel in a ___________ circuit.
2. A ___________ circuit has more than one path for current to flow.
3. In a series circuit, the total voltage supplied by the power supply is
__________________ among the loads.
4. The voltage drop across any component is the difference in voltage
referenced to _______________ between the two terminals of the
component.
5. When a parallel circuit is connected to a constant voltage source, the
same amount of voltage is available to each ________ of the circuit.
6. Most AC wiring circuits in buildings use _________ circuits so the
loads can all receive the same voltage.
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SEGMENT 3
CURRENT MEASUREMENT
OBJECTIVE 7
DEFINE CURRENT AND GIVE ITS UNITS OF MEASUREMENT
Electrical Current is the flow of electrons through a circuit. It carries the electrical energy to the point of use.
Current is measured in units of amperes. The abbreviation symbol (amps) is an
A following a numeric value. For example, a current of 5 amperes is written as 5A.
Sometimes current values can be very small, such as 1/1000th of an amp
(0.001A). In this case, the unit used is milli-amp or mA (the prefix milli means
1/1000th). For example, 0.001A can be written as 1mA.
Current can either flow in one direction (DC) or alternately in two directions
(AC).
OBJECTIVE 8
DESCRIBE THE FUNCTION OF TWO TYPES OF AMMETERS
AND GIVE THEIR SCHEMATIC SYMBOL
An ammeter is a device that measures electrical current. It can have an analog
display, like the one in figure 34, or a digital display.
Figure 34. An Analog Ammeter
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Ammeters are often specified in circuits. Figure 35 shows the schematic
symbol for an ammeter.
A
Figure 35. Schematic Symbol for an Ammeter
OBJECTIVE 9
DESCRIBE HOW TO USE AN AMMETER TO MEASURE CURRENT
To measure current through a component, the ammeter is placed in series with
the component, as shown in figure 36. This is different than measuring voltage
where a meter’s leads are connected across the component (in parallel).
Incorrect connection of an ammeter can result in damage to the ammeter and/
or the power supply. Always make sure the ammeter is connected in series.
MEASURING CURRENT
+
MEASURING VOLTAGE
+
CURRENT
METER
R2
R1
A
CURRENT
V
Figure 36. Measuring Current vs. Measuring Voltage
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SKILL 4
USE A DMM TO MEASURE THE ELECTRICAL CURRENT
Procedure Overview
In this procedure, you will measure the current in a circuit using a DMM.
This is the same measurement you made in the simulation.
CAUTION
When you measure the current you must put the DMM in series with the
devices in the circuit. This means that the current will actually flow through
the DMM and on through the rest of the circuit. Basically, the meter becomes
another component of the circuit.

1. Perform the following substeps to measure DC current with a DMM.
A. Turn the Function/Range Switch of the DMM to the OFF position.
B. Plug the red test lead into the (10A) terminal.
C. Plug the black test lead into the terminal labeled COM.
D. Rotate the Function/Range switch to the 10A position in the DC Current
section.
CAUTION
If the current is higher than the maximum rating of the DMM, damage to
the DMM could occur. Most DMM’s have a protective device inside to protect
the internal components in this case. We will discuss circuit protection in more
detail later.
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
2. Connect the DMM in the circuit, as shown in figure 37.
+
SOURCE SELECT
12V
AC
DC
LAMP
24V
12V
12V
A
30XR
NON
CONTACT
VOLTAGE
MIN MAX
V
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
10A
CAT
CAT
A
LAMP
MODULE
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
Figure 37. Measuring Current

3. Place the AC-DC selector switch on the T7017 power supply in the DC
position.

4. Turn on the power supply and record the current reading.
Current Reading ________________________________________ (Amps)

You should observe that the circuit is approximately 0.1 Amps.

5. Turn off the power supply and the DMM.

6. Disconnect the circuit.
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SKILL 5
USE A DMM TO MEASURE CURRENT IN SERIES
AND PARALLEL CIRCUITS
Procedure Overview
In this procedure, you will use a DMM to measure current in both a series
and a parallel circuit. This procedure should help you see how current reacts in
series and parallel circuits.

1. Perform the following substeps to measure the current of a series circuit with
a DMM.
A. Turn the Function/Range switch of the DMM to the OFF position.
B. Plug the red test lead into the 10A (right) terminal.
C. Plug the black test lead into the COM terminal.
D. Turn the Function/Range switch to the 10A position in the DC Current
section.


2. Connect the series circuit with the DMM connected as shown in figure 38.
This allows you to measure the current between the positive terminal of the
power supply and R1.
R1 = 10
A
+
12V
LAMP
Figure 38. Series Circuit

3. Turn on the power supply and record the current reading.
Current Reading = ______________________________________ (Amps)


It should be 0.1 Amps.
4. Turn off the power supply.
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
5. Now, move the meter between R1 and the lamp, as shown in figure 39.
R1 = 10
+
A
12V
LAMP
Figure 39. Series Circuit

6. Turn on the power supply and record the current reading.
Current Reading = _______________________________________ (Amps)

The current at this point should be the same as in step 3 because the same
amount of current flows through each component in a series circuit.

7. Turn off the power supply.

8. Now, place the meter between the lamp and the ground terminal of the power
supply, as shown in figure 40.
R1 = 10
+
12V
A
LAMP
Figure 40. Series Circuit
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
9. Turn on the power supply and record the current reading.
Current Reading = _______________________________________ (Amps)

The current at this point should be the same as in steps 3 and 6.

This demonstrates that the current in a series circuit is the same at any point
in the circuit.



10. Turn off the power supply and disconnect the circuit.
In the following steps, you will measure the current at different locations in a
parallel circuit.
11. Perform the following substeps to measure the current between the positive
terminal of the power supply and the parallel loads.
A. Connect the parallel circuit, as shown in figure 41.
A
BRANCH
1
+
12V
R1 = 10
BRANCH
2
LAMP
Figure 41. A Parallel Circuit
B. Turn on the power supply and record the current reading.
Current Reading = ____________________________________ (Amps)
The current should be approximately 1.58 amps.
The current measurement at this point is the total current for the circuit.
C. Turn off the power supply.
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
12. Perform the following substeps to measure the current in branch 1 of the
parallel circuit.
A. Place the meter in branch 1, as shown in figure 42.
BRANCH
1
+
BRANCH
2
R1=
10
12V
LAMP
A
Figure 42. Parallel Circuit
B. Turn on the power supply and record the reading.
Branch 1 Current Reading = ____________________________ (Amps)
The current in branch 1 should be less than the current you measured in
step 11. Since current is split between the branches of a parallel circuit,
this is only part of the total current in this circuit. The remainder of the
current should be flowing in the other branch.
C. Turn off the power supply.
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
13. Perform the following substeps to measure the current in branch 2 of the
circuit.
A. Place the meter between the lamp and the ground terminal of the power
supply, as shown in figure 43.
To do this, you will need to disconnect the wire between the lamp and the
ground terminal.
Placing the meter here allows you to measure the current that is running
through the lamp in branch 2.
BRANCH
1
LAMP
+
12V
BRANCH
2
R1=
10
A
Figure 43. Parallel Circuit
B. Turn on the power supply and record the reading.
Branch 2 Current Reading = ____________________________ (Amps)
The reading should again be less than the reading from step 11. The
current here is the remaining portion of the total current that is not flowing
through branch 1.
The amount of the total current that flows through each branch of a parallel
circuit depends on the resistance that is present in each branch, as you will
learn later.
C. Turn off the power supply.

14. Turn off the DMM and remove the test leads.

15. Disconnect the circuit and store all components.
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OBJECTIVE 10
DESCRIBE THE CURRENT CHARACTERISTICS IN SERIES
AND PARALLEL CIRCUITS
The current in a series circuit flows from the positive terminal of the power
supply to the negative terminal through each component in the circuit. Unlike
voltage, the current does not change as it flows through a series circuit. The same
amount of current flowing from the power supply’s positive terminal flows through
each component, as shown in figure 44.
CURRENT
+
R1
R2
R3
Figure 44. Loads in Series
While it is common to connect input devices in series, it is not common to
connect loads in series. One reason is that if one of the loads fails while the circuit
is in operation, all of the loads will lose power.
SOURCE
SOURCE
Figure 45. Removing a Lamp from a Series Circuit
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Many older Christmas tree light strings were connected in series. When one
light burned out, they were all out. You had to find out which light was burned out
and replace it.
In contrast, the current in a parallel circuit is divided among the branches of
the circuit, as shown in figure 46. The amount of current that flows in each branch
depends on the amount of resistance in that branch.
+
LOAD
1
BRANCH
1
LOAD
2
BRANCH
2
LOAD
3
BRANCH
3
Figure 46. Loads in Parallel
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If loads are connected in parallel and one fails, the others will continue to
work, as shown by the lamps in figure 47. This is because the same current does
not flow through each branch. For this reason, newer strings of Christmas lights
are connected in parallel.
PICTORIAL
OPEN FILAMENT
DIAGRAM
Figure 47. A Typical Parallel Light Circuit
Most circuits in commercial and residential buildings are wired in parallel.
Therefore, all of the outlets and sockets do not require something to be plugged
into them to complete the circuit. If series wiring is used, each outlet and socket
would need to have something plugged into it and be turned on to complete the
circuit.
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Activity 3. Characteristics in Series and Parallel Circuits
Procedure Overview
In this procedure, you will connect lamps in series and parallel and observe
the characteristics of each. This will show you how current flows in series and
parallel circuits.

1. Connect the series load circuit shown in figure 48.
SOURCE SELECT
SCHEMATIC
AC
+
DC
24V
12V
12V
+
-
24V
LAMP 1
LAMP
MODULE
LAMP
MODULE
LAMP 2
LAMP 3
LAMP
MODULE
Figure 48. Three Loads in Series

2. Place the AC/DC selector switch in the DC position.

3. Turn on the power supply and observe the lamps.
Lamp 1 Status __________________________________________(On/Off)
Lamp 2 Status __________________________________________(On/Off)
Lamp 3 Status __________________________________________(On/Off)

All three lamps should be on, but they should be dim. The current is running
through all three lamps because the circuit path is complete.
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

4. Now, turn off the power supply and let the bulbs cool off.
Remove the center lamp from its socket. To remove the bulb, twist it
counterclockwise and lift up, as shown in figure 49.
CAUTION
ALWAYS TURN OFF THE POWER BEFORE YOU CHANGE ANY
COMPONENTS IN AN ELECTRICAL CIRCUIT!
HOLD THE
LAMP BY
THE GLASS
LAMP
BASE
LAMP
SOCKET
2. LIFT THE
BULB OUT
BAYONET
SLOT
BRACKET
TAB
1. TWIST THE LAMP
COUNTER CLOCKWISE
Figure 49. Lamp Removed from its Socket

5. Turn on the power supply on and observe the other lamps.
Lamp 1 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)

The other lamps should be off. This occurs because the current path has been
broken by removing one of the components. This is one reason why you
shouldn’t use series loads.
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6. Turn off the power supply and put the lamp back into its socket.

Replacing the lamp is done by pushing it down into the socket and turning it
clockwise until it locks into place.

7. Turn on the power supply again and observe the lamps.

Lamp 1 status __________________________________________(On/Off)
Lamp 2 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)
The lamps should all come back on.


8. Turn off the power supply.

9. Now connect the parallel load circuit shown in figure 50.
SOURCE SELECT
AC
SCHEMATIC
DC
24V
12V
+
-
+
12V
LAMP
1
LAMP
2
LAMP
3
24V
LAMP
MODULE
LAMP
MODULE
LAMP
MODULE
Figure 50. Loads Connected in Parallel

10. Turn on the power supply and observe the lamps.
Lamp 1 Status __________________________________________(On/Off)
Lamp 2 Status __________________________________________(On/Off)
Lamp 3 Status __________________________________________(On/Off)

All three lamps should be on. The current is split between the three lamps.

11. Turn off the power supply.

12. Wait about 30 seconds for the bulbs to cool and then remove lamp 1 from its
socket.
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
13. Turn on the power supply and observe the remaining lamps.
Lamp 2 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)

Both lamps should still be on at the same brightness. The current is now split
between the remaining branches of the circuit.

14. Turn off the power supply.

15. Replace lamp 1 in the circuit, turn on the power supply and observe the lamps.
Lamp 1 status __________________________________________(On/Off)
Lamp 2 status __________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)


All three should be on again.
16. Remove and replace lamp 2 and 3 separately and observe the results.

Make sure you let the bulbs cool before you remove them and remember to
turn off the power supply off when removing or replacing the bulbs.

The lamps that remain in the circuit should continue to burn even though one
of the lamps is removed because the current continues to flow in the other
branches.

17. Turn off the power supply.

18. Replace lamp 2 with the fan. Be sure to observe the polarity of the fan when
you connect it.

19. Operate the circuit and observe the status of the devices.
Lamp 1 status __________________________________________(On/Off)
Fan status _____________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)

All devices should be on.

20. Turn off the power supply.

21. Wait about 30 seconds for the lamps to cool and then remove lamp 1 from its
socket.

22. Turn on the power supply and observe the remaining devices.
Fan status _____________________________________________(On/Off)
Lamp 3 status __________________________________________(On/Off)
The other devices should remain on.

23. Turn off the power supply.

24. Place lamp back in its socket.

25. Disconnect the circuit and store all components.
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SEGMENT 3
SELF REVIEW
1. Current is measured in units called ________.
2. ___ is the abbreviation symbol for current.
3. When measuring current, the ammeter must be connected in _______
with the components of the circuit.
4. The current in a(n) ________ circuit flows from the positive terminal
of the supply to the negative terminal through each component in a
circuit.
5. The current in a(n) __________ circuit is divided among the branches
of the circuit.
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SEGMENT 4
RESISTANCE MEASUREMENT
OBJECTIVE 11
DEFINE RESISTANCE AND GIVE ITS UNITS OF MEASUREMENT
Resistance is the measure of a component’s ability to resist the flow of current
in a circuit. When current passes through a component that has resistance, the
current flow is slowed.
The units of measure for resistance are ohms. Ohm is abbreviated by the uppercase Greek letter omega (). For example, a 30 ohm resistor is written as R = 30.
Many resistors have a very high resistance. These higher values are usually
measured in kilo-ohms (K) which means 1000 times the value, or mega-ohms
(M) which is 1,000,000 times the value. For example, a 15K resistor is 15,000
ohms.
OBJECTIVE 12
DESCRIBE THE FUNCTION OF TWO TYPES OF OHMMETERS AND
GIVE THEIR SCHEMATIC SYMBOL
An ohmmeter is a device that measures the resistance between two points in an
electrical current. An ohmmeter can also be either analog or digital.
Figure 51 shows the schematic symbol for an ohmmeter.
Figure 51. Schematic Symbol for a Ohmmeter
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OBJECTIVE 13 DESCRIBE HOW TO USE AN OHMMETER TO MEASURE RESISTANCE
To measure resistance, the test leads of the ohmmeter are placed in parallel
with the component to be measured. The test lead connections for measuring resistance are the same as for measuring voltage. You measure across the component as
shown in figure 52. It does not matter which lead is connected to each side of the
component. If the component is connected in a circuit, you have to make resistance
measurements with the power to the circuit turned off to get an accurate measurement. In this case, the ohmmeter is measuring the resistance of resistor R1.
Notice that resistor R1 is not connected in a circuit. You can measure the
resistance of any component this way. Also, it does not matter how the leads are
connected to the component since resistance has no polarity.
R1
Figure 52. Measuring Component Resistance
To measure a component when it is connected in a circuit you should always
turn off the power and disconnect one terminal of the component from the circuit, as
shown in figure 53. Otherwise, you will get an erroneous resistance measurement.
+
R1
R2
R3
DISCONNECTED
TERMINAL
Figure 53. Measuring Resistance in a Circuit
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SKILL 6
USE A DMM TO MEASURE THE RESISTANCE OF A COMPONENT
Procedure Overview
In this procedure, you will measure the resistance of various loads with a
DMM. The loads do not have to be operating in or even connected in a circuit
for you to measure the resistance.

1. Perform the following substeps to measure resistance with the DMM.
A. Turn the Function/Range Switch to the OFF position.
B. Plug the red test lead into the (V) terminal.
C. Plug the black test lead into the terminal labeled COM.
D. Rotate the Function/Range switch to the 200 position in the Resistance
() section.

2. Place one test lead on one terminal of the lamp module and the other test lest
on the other terminal, as shown in figure 54.
30XR
LAMP MODULE
SCHEMATIC
REPRESENTATION
NON
CONTACT
VOLTAGE
MIN MAX
V
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
A
mA
RED
LEAD
BLACK
LEAD
10 A
200m
2m 20m
V
COM
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
Figure 54. Measuring Resistance

3. Record the value of resistance displayed by DMM.
Resistance Value ________________________________________ (Ohms)

The resistance should be approximately 14 ohms.
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
4. Measure the resistance of one of the resistors in the same manner that your
measured the lamp.
Resistance Value ________________________________________ (Ohms)


The resistor modules should have the resistance value printed on them (either
10 ohms or 25 ohms). Your measurement value should be very close to that
value.
5. Turn off the DMM and remove the test leads.
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OBJECTIVE 14
DESCRIBE THE RESISTANCE CHARACTERISTICS
IN SERIES AND PARALLEL CIRCUITS
When loads are connected in series, their individual resistances add together to
increase the total resistance in the circuit. As shown in figure 55, the resistance of
the circuit is larger with three resistors in series than with just one resistor.
R1 = 10
R1 = 10
R2 =
10
TOTAL RESISTANCE
10
R3 = 10
TOTAL RESISTANCE
30
Figure 55. Series Resistances Increase Total Resistance
However, when loads are connected in parallel, the total amount of resistance
actually decreases when more resistors are added. In figure 56, the total resistance
of three 10 resistors in parallel is only 3.33 while the total resistance of one
resistor is 10. You will learn more about resistance in series and parallel circuits
in the next LAP.
R1=
10
TOTAL RESISTANCE
10
R1=
10
R2=
10
R3=
10
TOTAL RESISTANCE
3.33
Figure 56. Parallel Resistance Decreases Total Resistance
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SKILL 7
MEASURE THE RESISTANCE IN SERIES AND PARALLEL CIRCUITS
Procedure Overview
In this procedure, you will measure the resistance of each component in
series and parallel circuits. Then you will also measure the total resistance of
the circuits. This will demonstrate the resistance characteristics of loads in
series and parallel will have different effects on the total resistance.

1. Connect the series circuit shown in figure 57.
+
12V
R1
R2
R3
Figure 57. Series Circuit

2. Perform the following substeps to measure the resistance of each load.
A. Disconnect the circuit from the positive terminal of the power supply.
Whenever you are taking resistance measurements in a circuit, it is a
good practice to disconnect the circuit from the power supply. This keeps
the circuit from being accidentally energized while you are making
measurements.
CAUTION
DO NOT make resistance measurements in a circuit if the power is on. The
meter can be damaged.
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B. Set the DMM to measure resistance.
C. Disconnect the terminals of load 1 from the circuit.
D. Measure the resistance across load 1 (R1).
Resistance Load 1 = __________________________________ (Ohms)
Load 1 should be approximately 10 Ohms (if the 10-Ohm resistor) or 25
Ohms (if the 25-Ohm resistor).
E. Reconnect the load’s terminal to the circuit.
F. Repeat substeps B-E to measure the resistance across load 2 (R2).
Resistance Load 2 = __________________________________ (Ohms)
Load 2 should be approximately 10 Ohms (if the 10-Ohm resistor) or 25
Ohms (if the 25-Ohm resistor).
G. Repeat substeps B-E to measure the resistance across the load 3 (R3).
Resistance Load 3 = __________________________________ (Ohms)
Load 3 should be approximately 10 Ohms (if the 10-Ohm resistor) or 25
Ohms (if the 25-Ohm resistor).

3. Now measure the total resistance of the circuit, as shown in figure 58.
Measured total resistance = _______________________________ (Ohms)
+
12V
R1
R2
R3
OPEN THE
CIRCUIT
HERE
TEST
LEAD
TEST
LEAD
Figure 58. Measuring Total Resistance


The measured total resistance should be higher than each of the three
individual resistances. Resistances in series circuits add together to increase
the total resistance of the circuit.
4. Disconnect the circuit.
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
5. Connect the parallel circuit shown in figure 59.
SOURCE SELECT
AC
SCHEMATIC
DC
24V
12V
12V
+
12V
R1
R2
R3
R1 = 10
BRANCH
1
10 RESISTOR
OHM MODULE
R2 = 25
BRANCH
2
R3 = 25
BRANCH
3
25 RESISTOR 25 RESISTOR
OHM MODULE OHM MODULE
Figure 59. Parallel Circuit

6. Perform the following substeps to measure the resistance of each branch of
the parallel circuit in figure 59.
A. Disconnect the wire leading from the negative terminal of the power
supply to R1, as figure 60 shows.
When you measure the resistance of a branch in a parallel circuit you must
disconnect one side of the branch from the circuit.
B. Measure the resistance across R1, as shown in figure 60.
R1 = _______________________________________________ (Ohms)
The resistance of R1, which is the resistance of branch 1, is approximately
10 ohms.
+
R1
R2
R3
DISCONNECTED
Figure 60. Measurement of Resistance in a Parallel Circuit
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C. Reconnect the wire from R1 to the ground terminal.
D. Repeat substeps A-C to measure the resistance in branch 2 (resistor R2).
R2 = _______________________________________________ (Ohms)
The resistance of R2, which is the resistance of branch 2, is approximately
25 ohms.
E. Repeat substeps A-C to measure the resistance in branch 3 (resistor 3).
R3 = _______________________________________________ (Ohms)
The resistance of R3, which is the resistance of branch 3, is approximately
25 ohms.

7. Measure the total resistance across the entire circuit, as shown in figure 61.
NOTE
Make sure that the power supply IS NOT ON.
CIRCUIT
DISCONNECTED
+
12V
R1 = 10
R2 = 25
R3 = 25
Figure 61. Total Resistance Measurement in a Parallel Circuit
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
8. Record the total resistance reading.
RT = _________________________________________________ (Ohms)

The total resistance of the three loads in parallel should be approximately 5.6
ohms. This value is lower than the lowest resistance branch (branch 1) of the
circuit.

In fact, the total resistance of any parallel circuit is always lower than the
resistance of the branch with the least resistance.

As you continue to add branches to a parallel circuit, the overall resistance
will continue to drop. If you remove a branch from a parallel circuit, the
overall resistance will increase.


9. Disconnect R3 from the circuit (remove a branch).
10. Measure the total resistance of the circuit across R1 and R2, as shown in
figure 62.
SCHEMATIC
DISCONNECTED
+
12V
R1
R2
Figure 62. Total Resistance Measured with R3 Removed

11. Record the total resistance reading.
RT = _________________________________________________ (Ohms)

The total resistance should now be 7.14 ohms. This is higher than with the
three resistors in parallel. However, the total resistance is still lower than the
lowest individual resistance (10 ohms).

12. Disconnect the circuit and store all components.

13. Turn off the DMM and remove the test leads.
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OBJECTIVE 15
DESCRIBE TWO METHODS OF MEASURING CONTINUITY
Continuity describes a situation in which there is a continuous or complete
path for current to flow in an electrical circuit.
Since all electrical components in a circuit are connected with a conductor of
some kind (wires or conductive traces on a printed circuit board), wires must have
continuity or the circuit will not operate.
BATTERY
WIRE
SWITCH
INDICATOR LAMP
Figure 63. A Circuit Connected with Wires
NOTE
Continuity does not represent zero resistance. Even a short wire contains
some resistance.
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A DMM can be used to test for continuity, sometimes in more than one way.
Two methods are:
• Measuring Resistance
• Using a Continuity Tester
Measuring Resistance
Ideally, there should be no resistance in a conductor. However, everything
actually has at least a small amount of resistance. If a conductor has continuity,
the display shows a very small resistance value such as 0.01 ohms. If the display
shows an out-of-range indication, there is an open in that conductor and there is no
continuity. An open has infinite resistance.
NOTE
One important thing to remember is that the longer the wire is, the higher
the resistance is going to be.
Using a Continuity Tester
A continuity tester, a function which many DMM’s have, indicates continuity
with a buzzing sound. When you place the leads across a conductor or component
that has continuity, a beeping or buzzing sound is made by the continuity tester.
The concept behind this is very simple. The continuity tester is composed of a
power source and a sounding device, as shown in figure 64. When the test leads are
applied across a conductor with continuity, the circuit is complete and the sounding
device sounds. The DMM you are using has this feature.
+
BUZZER
POWER
SUPPLY
TEST LEADS
Figure 64. Basic Design of a Continuity Tester
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SKILL 8
TEST THE CONTINUITY OF WIRES USING A DMM
Procedure Overview
In this procedure, you will test wires for continuity by measuring their
resistance and also by using the continuity tester on your DMM.

1. Perform the following substeps to check the continuity of the wires with the
T7017.
A. Prepare the DMM to measure resistance.
The Function/Range selector switch should be set to the lowest range in
the Resistance section (), which is 200.
B. Test the continuity of all the wires in the T7017 by measuring the resistance values.
A wire has continuity if the resistance reading on the DMM is approximately zero.
If you find any wires that do not have continuity or have a resistance
higher than 10 ohms, set them aside and notify your instructor.
30XR
NON
CONTACT
VOLTAGE
MIN MAX
CONDUCTOR WIRE
V
200
HOLD
600 OFF 600
200
20
RED
TEST
LEAD
BLACK
TEST
LEAD
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
Figure 65. Testing Continuity by Measuring Resistance
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C. Rotate the Function/Range switch clockwise to the continuity position, as
shown in figure 66.
30XR
NON
CONTACT
VOLTAGE
MIN MAX
CONDUCTOR WIRE
V
200
HOLD
600 OFF 600
200
20
RED
TEST
LEAD
BLACK
TEST
LEAD
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
Figure 66. Testing Continuity by Using Continuity Function
This is the position you must use for the continuity function. The small
dot with the arc shaped lines is the symbol used to represent the continuity
function.
D. Repeat substep B, including any wires that you might have found that
have a high resistance value.
When you perform this test, you should hear a beep if the wire has continuity. If you do not hear a beep, the wire does not have continuity.
BB227-BC02UEN ELECTRICAL MEASUREMENTS
Copyright © 2012 Amatrol, Inc.
73
SEGMENT 4
SELF REVIEW
1. Resistance is measured in units called __________.
2. The symbol for ohms is ___.
3. Since all electrical components in a circuit are connected with a
conductor of some kind, the conductor must have _________ or the
circuit will not operate.
4. A continuity tester is composed of a(n) _____________ and a sounding
device.
5. When measuring resistance, the user should measure ____________
the component.
6. When measuring the resistance of a component in a circuit, the user
should ____________ one side of the component from the circuit.
BB227-BC02UEN ELECTRICAL MEASUREMENTS
Copyright © 2012 Amatrol, Inc.
74