OBJECTIVES

2. OBJECTIVES After studying Chapter 10, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis). • Use a digital storage oscilloscope to measure voltage signals. • Interpret meter and scope readings and determine if the values are within factory specifications. • Explain time base and volts per division settings.

3. 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.

4. OSCILLOSCOPES FIGURE 10-1 (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.

5. OSCILLOSCOPES FIGURE 10-2 The display on a digital storage oscilloscope (DSO) displays the entire waveform from idle to wide-open 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)

6. 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 10-3 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.

7. OSCILLOSCOPE DISPLAY GRIDSetting 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.

8. OSCILLOSCOPE DISPLAY GRIDSetting 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.

9. OSCILLOSCOPE DISPLAY GRIDDC 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.

10. OSCILLOSCOPE DISPLAY GRIDAC 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.

11. OSCILLOSCOPE DISPLAY GRIDPulse 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.

12. OSCILLOSCOPE DISPLAY GRIDPulse Trains FIGURE 10-4 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)

13. OSCILLOSCOPE DISPLAY GRIDFrequency • 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).

14. OSCILLOSCOPE DISPLAY GRIDDuty Cycle • Duty cycle refers to the percentage of on-time of the signal during one complete cycle. FIGURE 10-5 (a) A scope representation of a complete cycle showing both on-time and off-time. (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)

15. OSCILLOSCOPE DISPLAY GRIDPulse Width • The pulse width is a measure of the actual on-time measured in milliseconds. • Fuel injectors are usually controlled by varying the pulse width. FIGURE 10-6 Most automotive computer systems control the device by opening and closing the ground to the component. (Courtesy of Fluke Corporation)

16. 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.

17. OSCILLOSCOPE DISPLAY GRID FIGURE 10-7 (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).

18. OSCILLOSCOPE DISPLAY GRIDUsing 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.

19. OSCILLOSCOPE DISPLAY GRIDMeasuring 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.

20. OSCILLOSCOPE DISPLAY GRIDMeasuring Battery Voltage with a Scope FIGURE 10-8 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)

21. 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 10-9 A typical graphing multimeter.

22. CAN SCOPES MEASURE CURRENT? FIGURE 10-10 The fused jumper wire is connected to terminals 30 and 87 of the fuel pump relay socket. The current probe is shown clamped around the wire and the electronics in the probe convert the current reading into a millivolt signal that is used by the DSO to display the changing current waveform.

23. SUMMARY • Analog oscilloscopes use a cathode ray tube to display voltage patterns. • The waveforms shown on an analog oscilloscope cannot be stored for later viewing. • A digital storage oscilloscope (DSO) creates an image or waveform on the display by connecting thousands of dots captured by the scope leads. • An oscilloscope display grid is called a graticule. Each of the 8 10 dividing boxes is called a division. • Setting the time base means establishing the amount of time each division represents.

24. SUMMARY • Setting the volts per division allows the technician to view the entire, or just part of, the waveform. • DC and AC coupling are two selections that can be made to observe a waveform. • A graphing multimeter is not capable of capturing short duration faults but can display usable waveforms. • Oscilloscopes display voltage over time. A DSO can capture and store a waveform for viewing later.

25. REVIEW QUESTIONS • What are the differences between an analog and a digital oscilloscope? • What is the difference between DC coupling and AC coupling? • Why are DC signals that change called pulse trains? • What is the difference between an oscilloscope and a graphing multimeter?

26. CHAPTER QUIZ • 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

27. CHAPTER QUIZ • 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

28. CHAPTER QUIZ 2. An oscilloscope display is called a _____. • Grid • Graticule • Division • Box

29. CHAPTER QUIZ 2. An oscilloscope display is called a _____. • Grid • Graticule • Division • Box

30. 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

31. 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

32. CHAPTER QUIZ 4. Setting the time base to 50 ms per division will allow the technician to view a waveform how long in duration? • 50 ms • 200 ms • 400 ms • 500 ms

33. CHAPTER QUIZ 4. Setting the time base to 50 ms per division will allow the technician to view a waveform how long in duration? • 50 ms • 200 ms • 400 ms • 500 ms

34. 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? • 0.5 V/division • 1.0 V/division • 2.0 V/division • 5.0 V/division

35. 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? • 0.5 V/division • 1.0 V/division • 2.0 V/division • 5.0 V/division

36. 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

37. 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? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

38. CHAPTER QUIZ 7. Voltage signals (waveforms) that do not go below zero are called _____. • AC signals • Pulse trains • DC signals • DC coupled signals

39. CHAPTER QUIZ 7. Voltage signals (waveforms) that do not go below zero are called _____. • AC signals • Pulse trains • DC signals • DC coupled signals

40. CHAPTER QUIZ 8. Cycles per second are expressed in _____. • Hertz • Duty cycle • Pulse width • Slope

41. CHAPTER QUIZ 8. Cycles per second are expressed in _____. • Hertz • Duty cycle • Pulse width • Slope

42. CHAPTER QUIZ 9. Oscilloscopes use what type of lead connector? • Banana plugs • Double banana plugs • Single conductor plugs • BNC

43. CHAPTER QUIZ 9. Oscilloscopes use what type of lead connector? • Banana plugs • Double banana plugs • Single conductor plugs • BNC

44. CHAPTER QUIZ 10. A digital meter that can show waveforms is called a _____. • DVOM • DMM • GMM • DSO

45. CHAPTER QUIZ 10. A digital meter that can show waveforms is called a _____. • DVOM • DMM • GMM • DSO