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OBJECTIVESAfter studying Chapter 9, the reader will be able to:1. Prepare for ASE Electrical/Electronic Systems (A6)certification test content area “A” (GeneralElectrical/Electronic System Diagnosis).2. Use a digital storage oscilloscope to measurevoltage signals.3. Interpret meter and scope readings and determineif 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 EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPES An oscilloscope (usually called a scope) is avisual voltmeter with a timer (clock) that showswhen a voltage changes. An analog scope uses a cathode ray tube (CRT)similar to a television screen to display voltagepatterns.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPESFIGURE 9-1 (a) On an analogscope, the voltage measured at thethrottle position signal wire isdisplayed on a horizontal line atabout 0.5 volt. (b) As the throttle isopened, the horizontal linerepresenting the voltage increases.(c) At wide-open throttle (WOT), thehorizontal line indicates about 4.5volts.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPESFIGURE 9-2 The display on a digitalstorage oscilloscope (DSO) displaysthe entire waveform from idle to wideopen throttle and then returns to idle.The display also indicates themaximum (4.72 V) and the minimum(680 mV or 0.68 V) reading. Thedisplay does not show anything untilthe throttle is opened, because thescope has been set up to only startdisplaying a waveform after a certainvoltage level has been reached. Thisvoltage is called the trigger. (Courtesyof Fluke Corporation)Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRID A typical scope face haseight grids vertically (upand down) and ten gridshorizontally. The grid lines on the scopescreen are used as areference scale, which iscalled a graticule.FIGURE 9-3 An automotive oscilloscope (scope)is of the same construction as a cathode raytube (CRT) or television screen. An automotiveoscilloscope is a visual voltmeter. The higher upa trace (line) on the scope, the higher thevoltage. The scope illustrates time from left toright. The longer the horizontal line, the longerthe amount of time.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDSetting the Time Base Most scopes use 10 graticules from left to right onthe display. Setting the time base means setting how muchtime 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 EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDSetting the Volts per Division The vertical scale has eight divisions. If each division is set to equal 1 volt, the display willshow 0 to 8 volts. This is okay in a 0 to 5 volt variable sensor such asa throttle position (TP) sensor. The volts per division (V/div) should be set so thatthe entire anticipated waveform can be viewed.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDDC Coupling DC coupling is the most used position on a scopebecause it allows the scope to display alternatingcurrent (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 DCcomponent.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDAC Coupling When the AC coupling position is selected, acapacitor is placed into the meter lead circuit, whicheffectively blocks all DC voltage signals but allowsthe AC portion of the signal to pass and bedisplayed.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDPulse Trains A DC voltage that turns on and off in a series ofpulses is called a pulse train. Pulse trains differ from an AC signal in that they donot go below zero. An alternating voltage goes above and below zerovoltage.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDPulse TrainsFIGURE 9-4 A pulse train in anyelectrical signal that turns on andoff, or goes high and low in aseries of pulses. Igniter and fuelinjector pulses are examples of apulse train signal. (Courtesy ofFluke Corporation)Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDFrequency Frequency is the number of cycles per secondmeasured in hertz. Engine RPM signal is an example of a signal thatcan occur at various frequencies. At low engine speed, the ignition pulses occur fewertimes per second (lower frequency) than when theengine is operated at higher engine speeds (RPM).Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDDuty Cycle Duty cycle refers to the percentage of on-time of the signalduring 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 andnegative () symbol. This indicates that the meter started to record the percentage of on timewhen the voltage dropped (start of on-time). (Courtesy of Fluke Corporation)Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDPulse Width The pulse width is ameasure of the actual ontime measured inmilliseconds. Fuel injectors are usuallycontrolled by varying thepulse width.FIGURE 9-6 Most automotive computersystems control the device by openingand closing the ground to thecomponent. (Courtesy of FlukeCorporation)Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDExternal Trigger– An external trigger is when the trace starts when asignal 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 waveformmust have in order to start the display.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDFIGURE 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 EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDUsing Scope Leads Most scopes, both analog and digital, normally usethe same test leads. These leads usually attach to the scope through aBNC connector, a miniature standard coaxial cableconnector. BNC is an international standard that is used in theelectronics industry.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDMeasuring Battery Voltage with a Scope One of the easiest things to measure and observeon a scope is battery voltage. A lower voltage can be observed on the scopedisplay as the engine is started and a higher voltageshould be displayed after the engine starts.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OSCILLOSCOPE DISPLAY GRIDMeasuring Battery Voltage with a ScopeFIGURE 9-8 Battery voltage isrepresented by a flathorizontal line. In thisexample, the engine wasstarted and the battery voltagedropped to about 10 V asshown on the left side of thescope display. When theengine started, the generator(alternator) started to chargethe battery and the voltage isshown as climbing. (Courtesyof Fluke Corporation)Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

GRAPHING MULTIMETER A graphing multimeter,abbreviated GMM, is across between a digitalmeter and a digital storageoscilloscope. A graphing multimeterdisplays the voltage levelson a display and a digitalreadout.FIGURE 9-9 A typical graphing multimeter.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

SUMMARY1. Analog oscilloscopes use a cathode ray tube to displayvoltage patterns.2. The waveforms shown on an analog oscilloscope cannotbe stored for later viewing.3. A digital storage oscilloscope (DSO) creates an image orwaveform on the display by connecting thousands of dotscaptured by the scope leads.4. An oscilloscope display grid is called a graticule. Each ofthe 8 x 10 dividing boxes is called a division.5. Setting the time base means establishing the amount oftime each division represents.Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458