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  • Figure 43-1 A scope display allows technicians to take measurements of voltage patterns. In this example, each vertical division is 1 volt and each horizontal division is set to represent 50 milliseconds.
  • Figure 43-2 The display on a digital storage oscilloscope (DSO) displays the entire waveform of a throttle position (TP) sensor from idle to wide-open throttle and then returns to idle. The display also indicates the maximum reading (4.72 V) and the minimum (680 mV or 0.68 V). 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 or trigger point.
  • Chart 43-1 The time base is milliseconds (ms) and total time of an event that can be displayed.
  • Figure 43-3 Ripple voltage is created from the AC voltage from an alternator. Some AC ripple voltage is normal but if the AC portion exceeds 0.5 volt, then a bad diode is the most likely cause. Excessive AC ripple can cause many electrical and electronic devices to work incorrectly.
  • Figure 43-4 A pulse train is any electrical signal that turns on and off, or goes high and low in a series of pulses. Ignition module and fuel-injector pulses are examples of a pulse train signal.
  • Figure 43-5 (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 a percentage (%). 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).
  • Figure 43-6 Most automotive computer systems control the device by opening and closing the ground to the component.
  • Figure 43-7 A two-channel scope being used to compare two signals on the same vehicle.
  • Figure 43-8 (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—a trigger occurs at a falling (negative) edge of the signal (waveform).
  • Figure 43-9 Constant 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 alternator started to charge the battery and the voltage is shown as climbing.
  • Figure 43-10 A typical graphing multimeter that can be used as a digital meter, plus it can display the voltage levels on the display screen.

Halderman ch043 lecture Halderman ch043 lecture Presentation Transcript

  • OSCILLOSCOPES AND GRAPHING MULTIMETERS 43
  • Objectives
    • The student should 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.
  • Objectives
    • The student should be able to:
      • Interpret meter and scope readings and determine if the values are within factory specifications.
      • Explain time base and volts per division settings.
    View slide
  • TYPES OF OSCILLOSCOPES View slide
  • Types of Oscilloscopes
    • Terminology
      • Oscilloscope (usually called a scope): visual voltmeter with a timer that shows voltage changes
  • Types of Oscilloscopes
    • Terminology
      • Analog scopes: use a cathode ray tube (CRT) to display voltage patterns
  • Types of Oscilloscopes
    • Terminology
      • Digital scopes (DSO) commonly use a liquid crystal display (LCD) and take samples of the signals that can be stopped or stored
  • Types of Oscilloscopes
    • Terminology
      • A scope has been called “a voltmeter with a clock” because it captures and displays changing voltage levels and displays changes within a specific time period
  • Types of Oscilloscopes
    • Oscilloscope Display Grid
      • Scope faces: usually have eight or ten vertical grids and ten horizontal grids
  • Types of Oscilloscopes
    • Oscilloscope Display Grid
      • Graticule: transparent scale (grid) used for reference measurements commonly with 8 x 10 or 10 x 10 divisions
  • Types of Oscilloscopes
    • Oscilloscope Display Grid
      • NOTE: These numbers originally refer to the metric dimensions of the graticule in centimeters. Therefore, an 8 x 10 display would be 8 cm (80 mm or 3.14 in.) high and 10 cm (100 mm or 3.90 in.) wide.
  • Figure 43-1 A scope display allows technicians to take measurements of voltage patterns. In this example, each vertical division is 1 volt and each horizontal division is set to represent 50 milliseconds.
  • SCOPE SETUP AND ADJUSTMENTS
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Setting how much time will be displayed in each block (division)
      • Time base should be set to an amount of time that allows two to four events to be displayed
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Milliseconds (0.001 sec.) are commonly used in scopes when adjusting the time base
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly, including:
        • MAP/MAF sensors: 2 ms/div (20 ms total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly, including:
        • Network (CAN) communications network: 2 ms/div (20 ms total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly including:
        • Throttle position (TP) sensor: 100 ms per division (1 sec. total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly including:
        • Fuel injector: 2 ms/div (20 ms total)
        • Oxygen sensor: 1 sec. per division (10 sec. total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly including:
        • Primary ignition: 10 ms/div (100 ms total)
        • Secondary ignition: 10 ms/div (100 ms total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • Time per division settings can vary greatly including:
        • Voltage measurements: 5 ms/div (50 ms total)
  • Scope Setup and Adjustments
    • Setting the Time Base
      • NOTE: Increasing the time base reduces the number of samples per second.
  • Figure 43-2 The display on a digital storage oscilloscope (DSO) displays the entire waveform of a throttle position (TP) sensor from idle to wide-open throttle and then returns to idle. The display also indicates the maximum reading (4.72 V) and the minimum (680 mV or 0.68 V). 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 or trigger point.
  • Chart 43-1 The time base is milliseconds (ms) and total time of an event that can be displayed.
  • Scope Setup and Adjustments
    • Volts Per Division
      • Abbreviated V/div
      • Should be set so the entire anticipated waveform can be viewed
  • Scope Setup and Adjustments
    • Volts Per Division
      • Examples include:
        • Throttle position (TP) sensor: 1 V/div (8 V total)
        • Battery, starting and charging: 2 V/div (16 V total)
  • Scope Setup and Adjustments
    • Volts Per Division
      • Examples include:
        • Oxygen sensor: 200 mV/div (1.6 V total)
  • Scope Setup and Adjustments
    • Volts Per Division
      • Total voltage to be displayed exceeds the voltage range of the component being tested
  • DC AND AC COUPLING
  • DC and AC Coupling
    • DC Coupling
      • Most used position on a scope which allows both alternating current (AC) voltage signals and direct current (DC) voltage signals to be displayed
      • The AC part of the signal will ride on top of the DC component
  • DC and AC Coupling
    • AC Coupling
      • A capacitor is placed into the meter lead circuit, effectively blocking all DC voltage signals but allowing the AC signal be displayed
  • DC and AC Coupling
    • AC Coupling
      • Can be used to show output signal waveforms from sensors such as:
        • Distributor pickup coils
        • Magnetic wheel speed sensors
  • DC and AC Coupling
    • AC Coupling
      • Can be used to show output signal waveforms from sensors such as:
        • Magnetic crankshaft position sensors
        • Magnetic camshaft position sensors
  • DC and AC Coupling
    • AC Coupling
      • Can be used to show output signal waveforms from sensors such as:
        • Magnetic vehicle speed sensors
        • The AC ripple from an alternator
  • DC and AC Coupling
    • AC Coupling
      • NOTE: Check the instructions from the scope manufacturer for the recommended settings to use. Sometimes it is necessary to switch from DC coupling to AC coupling or from AC coupling to DC coupling to properly see some waveforms.
  • Figure 43-3 Ripple voltage is created from the AC voltage from an alternator. Some AC ripple voltage is normal but if the AC portion exceeds 0.5 volt, then a bad diode is the most likely cause. Excessive AC ripple can cause many electrical and electronic devices to work incorrectly.
  • PULSE TRAINS
  • Pulse Trains
    • Definition
      • Pulse train: voltage that turns on and off in a series of pulses
      • Pulse trains differ from AC signals because they do not go below zero
  • Figure 43-4 A pulse train is any electrical signal that turns on and off, or goes high and low in a series of pulses. Ignition module and fuel-injector pulses are examples of a pulse train signal.
  • Pulse Trains
    • Frequency
      • Number of cycles per second measured in hertz
  • Pulse Trains
    • Duty Cycle
      • Refers to the percentage of on-time of the signal during one complete cycle
  • Pulse Trains
    • Duty Cycle
      • Also called pulse-width modulation (PWM)
      • Can be measured in degrees
  • Figure 43-5 (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 a percentage (%). 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).
  • Pulse Trains
    • Pulse Width
      • A measure of the actual on-time measured in milliseconds
  • Figure 43-6 Most automotive computer systems control the device by opening and closing the ground to the component.
  • NUMBER OF CHANNELS
  • Number of Channels
    • Definition
      • The number of events, which require leads for each, is called a channel
        • A channel is an input to a scope
  • Number of Channels
    • Definition
      • Commonly available scopes include:
        • Single channel: capable of displaying only one sensor signal waveform at a time
  • Number of Channels
    • Definition
      • Commonly available scopes include:
        • Two channel: can display the waveform from two separate sensors or components at the same time
  • Number of Channels
    • Definition
      • Commonly available scopes include:
        • Four channel: allows the technician to view up to four different sensors or actuators on one display
  • Number of Channels
    • NOTE: Often the capture speed of the signals is slowed when using more than one channel.
  • Figure 43-7 A two-channel scope being used to compare two signals on the same vehicle.
  • TRIGGERS
  • Triggers
    • External Trigger
      • An external trigger is when the waveform starts when a signal is received from another external source rather than from the signal pickup lead
  • Triggers
    • Trigger Level
      • Trigger level is the voltage that must be detected by the scope before the pattern will be displayed
  • Triggers
    • Trigger Slope
      • The trigger slope is the voltage direction that a waveform must have in order to start the display
  • Triggers
    • Trigger Slope
      • The scope display indicates both a positive and a negative slope symbol
  • Figure 43-8 (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—a trigger occurs at a falling (negative) edge of the signal (waveform).
  • USING A SCOPE
  • Using a Scope
    • Using Scope Leads
      • Leads usually attach to the scope through a BNC connector (miniature standard coaxial cable connector)
  • Using a Scope
    • Using Scope Leads
      • Be sure to connect one lead to a good clean, metal engine ground
      • The probe attaches to the circuit or component being tested
  • Using a Scope
    • Measuring Battery Voltage With a Scope
      • A lower voltage can be observed as the engine is started and a higher voltage should be displayed after the engine starts
  • Using a Scope
    • CAUTION: Check the instructions for the scope being used before attempting to scope household AC circuits. Some scopes, such as the Snap-On MODIS, are not designed to measure high-voltage AC circuits.
  • Figure 43-9 Constant 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 alternator started to charge the battery and the voltage is shown as climbing.
  • GRAPHING MULTIMETER
  • Graphing Multimeter
    • A graphing multimeter (abbreviated GMM) is a cross between a digital meter and a digital storage oscilloscope
  • Graphing Multimeter
    • Voltage is displayed at two places:
      • On a display screen
      • In a digital readout
  • Figure 43-10 A typical graphing multimeter that can be used as a digital meter, plus it can display the voltage levels on the display screen.
  • GRAPHING SCAN TOOLS
  • Graphing Scan Tools
    • Many scan tools are capable of displaying the voltage levels captured by the scan tool through the data link connector (DLC)
      • Read and follow the instructions for the scan tool being used