Wrap-Up

Ready for Review

• Oscilloscopes allow the technician to view a waveform, to determine whether a component has failed.
• Analog and digital oscilloscopes each have their applications and uses.
• An oscilloscope is used to draw a picture within an electrical circuit.
• DMMs and oscilloscopes are used in specific situations.
• Computer-based oscilloscopes have more options.
• Big-box oscilloscopes and analyzers are not used as much anymore, because of the increased usage of smaller computer components.
• Oscilloscopes are useful to compare the operation of electrical components to a specified waveform.
• A disadvantage of an oscilloscope is its complexity, in setup and operation.
• Single-channel oscilloscopes can watch only one component at a time.
• Multichannel oscilloscopes can show different components on the same screen at the same time, for comparisons.
• Automatic time and voltage setup are available for most DSOs.
• Overriding the automatic specifications can cause the waveform to disappear from the scope screen.
• Using a trigger to allow the scope to start recording at specific times can maintain the waveform on the screen.
• The scope can direct the technician the wrong way when it is not setup correctly.
• Using cursors allows the technician to measure a waveform event on the screen, which will allow them to verify whether the operation is within specification.
• Coupling the signal on the oscilloscope helps to eliminate stray voltages within the waveform.
• Using channel presets helps start the waveform in a good position so that the technician can see the waveform.

Key Terms

cathode ray tube (CRT)  A high-vacuum tube in which cathode rays produce a luminous image on a fluorescent screen, which are used chiefly in televisions and computer terminals.

coupling  A direct connection to the circuit that allows all frequencies to pass.

cursor  A function that enables the user to measure quantity, time, and frequency between two points on the trace.

digital storage oscilloscope (DSO)  A scope that displays voltage over a time, allowing the technician to see the signal. The DSO has a very fast refresh rate and is able to catch even the smallest signal error or fault. A DSO connects to a circuit in the same manner as using a DMM to measure available voltage. Technicians become skittish around the DSO because it requires setting the voltage and time scales to display the signal correctly. There are many other features, including data recording and setting a trigger to start or stop recording.

oscilloscope (scope)  A test instrument used to display a waveform of voltage over time on a screen. These offer much higher resolutions and sample rates than GMMs.

scope channel  The ability to measure different waveforms at the same time so that comparisons can be made between each channel.

trigger  A setting on a DMM, GMM, or DSO that starts or stops a recording or signal display event. The trigger usually has several options that allow one-time or repeat functions.

Review Questions

1. Which one of the following is a disadvantage of using an oscilloscope?
   • The learning curve it takes to operate an oscilloscope.
   • Its inability to produce a waveform.
   • Its inability to express electrical information.
   • The false information that it displays.
2. All of the following statements with respect to oscilloscopes are true except:
   • Oscilloscopes allow the technician to display how the electrical component is operating.
   • Using the wrong scale on an oscilloscope can cause the waveform to be displayed incorrectly.
   • Oscilloscopes cannot view a glitch in an electrical component waveform.
   • Oscilloscopes can sometimes be combined with a scanner in one tool.
3. A falling edge waveform means the slope of the waveform is _________.
   • sloping
   • neutral
   • negative
   • positive
4. An analog oscilloscope does not have which one of the following functions?
   • The ability to record and store the waveform.
   • The ability to view the fault of the component.
   • The ability to change the voltage scale on the oscilloscope.
   • The ability to change the timeframe that the waveform is being shown in.
5. Setting the time base on an oscilloscope screen allows the technician to _________.
   • make the waveform different for the PCM
   • fit the whole waveform on one screen
   • scan the vehicle for codes from the PCM
   • determine whether the vehicle is working on 12 volts
6. Using a trigger helps the technician to do which of the following?
   • It transfers the waveform to a file.
   • It identifies fault related to the electrical system.
   • It does nothing.
   • It tells the scope when to start drawing the waveform.
7. When reading a square wave pattern, the technician should be looking for which one of the following?
   • Smooth edges of the square wave.
   • Crisp edges that show that it is on and then off.
   • A sine wave–style pattern that rolls smoothly.
   • The length of the square wave.
8. Scope and scan tools combos are a useful in a repair facility because they allow the technician to do which two things on one piece of equipment?
   • Query the PCM and view the waveform of the affected sensor.
   • Diagnose the vehicle by just plugging it in.
   • Explore the uses of both tools at the same time
   • Use the scope to view the waveform and the scanner to scan the vehicle for codes.
9. Filtering out the noise that is caused by other electrical components help the waveform to ___________.
   • appear clearer
   • change its amplitude
   • change its voltage
   • adapt to other wave lengths
10. A waveform that has a rising edge is said to have what type of slope?
    • Negative.
    • Neutral.
    • Positive.
    • Switching.

ASE Technician A/Technician B–Style Questions

1. Technician A says ground leads can be stacked on top of each other on the scope so that all channels can have ground. Technician B says a scope helps with understanding what a sensor is reading and sending back to the PCM. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says AC/DC voltage coupling eliminates the voltages that the technician doesn’t want to see. Technician B says triggers can be used to actuate sensors on the vehicle that it is trying to capture. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says that using a wiring schematic to determine the sensor’s position on the engine can help with diagnosing an issue. Technician B says that setting up the scope manually without knowing the intended waveform may cause the waveform to not appear on the screen. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says that using substandard test leads may lead to a corrupted signal on the oscilloscope. Technician B says grounding the test lead can produce a cleaner signal with minimal interference. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says the advantage of multichannel oscilloscopes is that they allow a technician to compare waveforms to discern similarities and differences. Technician B says signal noise is something that cannot affect the waveform being produced by the electrical component. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says an oscilloscope can be used to draw a picture of the electrical pulses that are causing the component to operate. Technician B says a scope and scanner combo can be beneficial because it is a complete tool. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says that setting the time base on the oscilloscope allows the technician to look at a voltage of the waveform. Technician B says the trigger is where the oscilloscope starts recording the waveform. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says computer-based lab oscilloscopes increase the capabilities of the scope in an electrical environment. Technician B says the big-box engine analyzers incorporate a scope and other equipment for diagnosing engine performance. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says when evaluating a sensor or electrical component, the technician should not operate the component when using the scope. Technician B says an oscilloscope allows the technician to view the graphical image of the electrical circuit. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says when filtering the scope signals, it helps to make the signal more viewable to the technician by removing interference from other components. Technician B says analog oscilloscopes are not quick enough to pick up some glitches produced by a failed sensor. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B