OBJECTIVES
After studying Chapter 9, the reader will be able to:
1. Prepare for ASE Electrical/Electronic Systems (A6)
certification test content area “A” (General
Electrical/Electronic System Diagnosis).
2. Use a digital storage oscilloscope to measure
voltage signals.
3. Interpret meter and scope readings and determine
if the values are within factory specifications.
4. Explain time base and volts per division settings.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPES
• An oscilloscope (usually called a scope) is a
visual voltmeter with a timer (clock) that shows
when a voltage changes.
• An analog scope uses a cathode ray tube (CRT)
similar to a television screen to display voltage
patterns.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPES
FIGURE 9-1 (a) On an analog
scope, the voltage measured at the
throttle position signal wire is
displayed on a horizontal line at
about 0.5 volt. (b) As the throttle is
opened, the horizontal line
representing the voltage increases.
(c) At wide-open throttle (WOT), the
horizontal line indicates about 4.5
volts.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPES
FIGURE 9-2 The display on a digital
storage oscilloscope (DSO) displays
the entire waveform from idle to wideopen throttle and then returns to idle.
The display also indicates the
maximum (4.72 V) and the minimum
(680 mV or 0.68 V) reading. The
display does not show anything until
the throttle is opened, because the
scope has been set up to only start
displaying a waveform after a certain
voltage level has been reached. This
voltage is called the trigger. (Courtesy
of Fluke Corporation)
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
• A typical scope face has
eight grids vertically (up
and down) and ten grids
horizontally.
• The grid lines on the scope
screen are used as a
reference scale, which is
called a graticule.
FIGURE 9-3 An automotive oscilloscope (scope)
is of the same construction as a cathode ray
tube (CRT) or television screen. An automotive
oscilloscope is a visual voltmeter. The higher up
a trace (line) on the scope, the higher the
voltage. The scope illustrates time from left to
right. The longer the horizontal line, the longer
the amount of time.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Setting the Time Base
• Most scopes use 10 graticules from left to right on
the display.
• Setting the time base means setting how much
time will be displayed in each block.
• A block is commonly referred to as a division.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Setting the Volts per Division
• The vertical scale has eight divisions.
• If each division is set to equal 1 volt, the display will
show 0 to 8 volts.
• This is okay in a 0 to 5 volt variable sensor such as
a throttle position (TP) sensor.
• The volts per division (V/div) should be set so that
the entire anticipated waveform can be viewed.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
DC Coupling
• DC coupling is the most used position on a scope
because it allows the scope to display alternating
current (AC) voltage signals and direct current (DC)
voltage signals present in the circuit.
• The AC part of the signal will ride on top of the DC
component.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
AC Coupling
• When the AC coupling position is selected, a
capacitor is placed into the meter lead circuit, which
effectively blocks all DC voltage signals but allows
the AC portion of the signal to pass and be
displayed.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Pulse Trains
• A DC voltage that turns on and off in a series of
pulses is called a pulse train.
• Pulse trains differ from an AC signal in that they do
not go below zero.
• An alternating voltage goes above and below zero
voltage.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Pulse Trains
FIGURE 9-4 A pulse train in any
electrical signal that turns on and
off, or goes high and low in a
series of pulses. Igniter and fuel
injector pulses are examples of a
pulse train signal. (Courtesy of
Fluke Corporation)
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Frequency
• Frequency is the number of cycles per second
measured in hertz.
• Engine RPM signal is an example of a signal that
can occur at various frequencies.
• At low engine speed, the ignition pulses occur fewer
times per second (lower frequency) than when the
engine is operated at higher engine speeds (RPM).
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Duty Cycle
• Duty cycle refers to the percentage of on-time of the signal
during one complete cycle.
FIGURE 9-5 (a) A scope representation of a complete cycle showing both on-time and offtime. (b) A meter display indicating the on-time duty cycle in percent (%). Note the trigger and
negative () symbol. This indicates that the meter started to record the percentage of on time
when the voltage dropped (start of on-time). (Courtesy of Fluke Corporation)
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Pulse Width
• The pulse width is a
measure of the actual ontime measured in
milliseconds.
• Fuel injectors are usually
controlled by varying the
pulse width.
FIGURE 9-6 Most automotive computer
systems control the device by opening
and closing the ground to the
component. (Courtesy of Fluke
Corporation)
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
External Trigger
– An external trigger is when the trace starts when a
signal is received from another (external) source.
Trigger Level
– The trigger level must be set to start the display.
Trigger Slope
– The trigger slope is the voltage direction that a waveform
must have in order to start the display.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
FIGURE 9-7 (a) A symbol for a positive trigger—a trigger occurs at a rising
(positive) edge of the signal (waveform). (b) A symbol for a negative trigger—
trigger occurs at a falling (negative) edge of the signal (waveform).
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Using Scope Leads
• Most scopes, both analog and digital, normally use
the same test leads.
• These leads usually attach to the scope through a
BNC connector, a miniature standard coaxial cable
connector.
• BNC is an international standard that is used in the
electronics industry.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Measuring Battery Voltage with a Scope
• One of the easiest things to measure and observe
on a scope is battery voltage.
• A lower voltage can be observed on the scope
display as the engine is started and a higher voltage
should be displayed after the engine starts.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OSCILLOSCOPE DISPLAY GRID
Measuring Battery Voltage with a Scope
FIGURE 9-8 Battery voltage is
represented by a flat
horizontal line. In this
example, the engine was
started and the battery voltage
dropped to about 10 V as
shown on the left side of the
scope display. When the
engine started, the generator
(alternator) started to charge
the battery and the voltage is
shown as climbing. (Courtesy
of Fluke Corporation)
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
GRAPHING MULTIMETER
• A graphing multimeter,
abbreviated GMM, is a
cross between a digital
meter and a digital storage
oscilloscope.
• A graphing multimeter
displays the voltage levels
on a display and a digital
readout.
FIGURE 9-9 A typical graphing multimeter.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
1. Analog oscilloscopes use a cathode ray tube to display
voltage patterns.
2. The waveforms shown on an analog oscilloscope cannot
be stored for later viewing.
3. A digital storage oscilloscope (DSO) creates an image or
waveform on the display by connecting thousands of dots
captured by the scope leads.
4. An oscilloscope display grid is called a graticule. Each of
the 8 x 10 dividing boxes is called a division.
5. Setting the time base means establishing the amount of
time each division represents.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
6. Setting the volts per division allows the technician
to view the entire, or just part of, the waveform.
7. DC and AC coupling are two selections that can be
made to observe a waveform.
8. A graphing multimeter is not capable of capturing
short duration faults but can display usable
waveforms.
9. Oscilloscopes display voltage over time. A DSO
can capture and store a waveform for viewing later.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
REVIEW QUESTIONS
1. What are the differences between an analog and a
digital oscilloscope?
2. What is the difference between DC coupling and
AC coupling?
3. Why are DC signals that change called pulse
trains?
4. What is the difference between an oscilloscope
and a graphing multimeter?
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. Technician A says an analog scope can store the
waveform for viewing later. Technician B says that
the trigger level has to be set on most scopes to
be able to view a changing waveform. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. An oscilloscope display is called a _____.
a)
b)
c)
d)
Grid
Graticule
Division
Box
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. A signal showing the voltage of a battery displayed
on an analog oscilloscope is being discussed.
Technician A says that the display will show one
horizontal line above the zero line. Technician B
says that the display will show a line sloping
upward from zero to the battery voltage level.
Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. Setting the time base to 50 ms per division will
allow the technician to view a waveform how long
in duration?
a)
b)
c)
d)
50 ms
200 ms
400 ms
500 ms
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. A throttle position sensor waveform is going to be
observed. At what setting should the volts per
division be set to see the entire waveform from 0
to 5 volts?
a)
b)
c)
d)
0.5 V/division
1.0 V/division
2.0 V/division
5.0 V/division
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Two technicians are discussing the DC coupling
setting on a DSO. Technician A says that the
position allows both the DC and AC signals of the
waveform to be displayed. Technician B says that
this setting allows just the DC part of the waveform
to be displayed. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. Voltage signals (waveforms) that do not go below
zero are called _____.
a)
b)
c)
d)
AC signals
Pulse trains
DC signals
DC coupled signals
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. Cycles per second are expressed in _____.
a)
b)
c)
d)
Hertz
Duty cycle
Pulse width
Slope
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. Oscilloscopes use what type of lead connector?
a)
b)
c)
d)
Banana plugs
Double banana plugs
Single conductor plugs
BNC
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. A digital meter that can show waveforms is called
a _____.
a)
b)
c)
d)
DVOM
DMM
GMM
DSO
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458