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  • Figure 42-1 A technician-made fused jumper lead, which is equipped with a red 10 ampere fuse. This fused jumper wire uses terminals for testing circuits at a connector instead of alligator clips.
  • Figure 42-2 A 12 volt test light is attached to a good ground while probing for power.
  • Figure 42-3 A test light can be used to locate an open in a circuit. Note that the test light is grounded at a different location than the circuit itself.
  • Figure 42-4 A continuity light should not be used on computer circuits because the applied voltage can damage delicate electronic components or circuits.
  • Figure 42-5 An LED test light can be easily made using low cost components and an old ink pen. With the 470 ohm resistor in series with the LED, this tester only draws 0.025 ampere (25 milliamperes) from the circuit being tested. This low current draw helps assure the technician that the circuit or component being tested will not be damaged by excessive current flow.
  • Figure 42-6 A logic probe connected to the vehicle battery. When the tip probe is connected to a circuit, it can check for power, ground, or a pulse.
  • Figure 42-7 Typical digital multimeter. The black meter lead always is placed in the COM terminal. The red meter test lead should be in the volt-ohm terminal except when measuring current in amperes.
  • Chart 42-1 Common symbols and abbreviations used on digital meters.
  • Figure 42-8 Typical digital multimeter (DMM) set to read DC volts.
  • Figure 42-9 (a) A typical autoranging digital multimeter automatically selects the proper scale to read the voltage being tested. The scale selected is usually displayed on the meter face.Note that the display indicates “4,” meaning that this range can read up to 4 volts.
  • Figure 42-9 (b) A typical autoranging digital multimeter automatically selects the proper scale to read the voltage being tested. The scale selected is usually displayed on the meter face.The range is now set to the 40 volt scale, meaning that the meter can read up to 40 volts on the scale. Any reading above this level will cause the meter to reset to a higher scale. If not set on autoranging, the meter display would indicate OL if a reading exceeds the limit of the scale selected.
  • Figure 42-10 Using a digital multimeter set to read ohms (Ω) to test this light bulb. The meter reads the resistance of the filament.
  • Figure 42-11 Many digital multimeters can have the display indicate zero to compensate for test lead resistance. (1) Connect leads in the V Ω and COM meter terminals. (2) Select the Ω scale. (3) Touch the two meter leads together. (4) Push the “zero” or “relative” button on the meter. (5) The meter display will now indicate zero ohms of resistance.
  • Figure 42-12 Measuring the current flow required by a horn requires that the ammeter be connected to the circuit in series and the horn button be depressed by an assistant.
  • Figure 42-14 An inductive ammeter clamp is used with all starting and charging testers to measure the current flow through the battery cables.
  • Figure 42-15 A typical mini clamp-on-type digital multimeter. This meter is capable of measuring alternating current (AC) and direct current (DC) without requiring that the circuit be disconnected to install the meter in series. The jaws are simply placed over the wire and current flow through the circuit is displayed.
  • Figure 42-17 Always look at the meter display when a measurement is being made, especially if using an autoranging meter.
  • Chart 42-2 A conversion chart showing the decimal point location for the various prefixes.
  • Chart 42-3 Sample meter readings using manually set and autoranging selection on the digital meter control.
  • Chart 42-3 (continued) Sample meter readings using manually set and autoranging selection on the digital meter control.
  • Figure 42-18 When reading AC voltage signals, a true RMS meter (such as a Fluke 87) provides a different reading than an average responding meter (such as a Fluke 88). The only place this difference is important is when a reading is to be compared with a specification.
  • Figure 42-19 This meter display shows 052.2 AC volts. Notice that the zero beside the 5 indicates that the meter can read over 100 volts AC with a resolution of 0.1 volt.
  • DIGITAL METER USAGE 1 For most electrical measurements, the black meter lead is inserted in the terminal labeled COM and the red meter lead is inserted into the terminal labeled V.
  • DIGITAL METER USAGE 2 To use a digital meter, turn the power switch and select the unit of electricity to be measured. In this case, the rotary switch is turned to select DC volts. (V)
  • DIGITAL METER USAGE 3 For most automotive electrical use, such as measuring battery voltage, select DC volts.
  • DIGITAL METER USAGE 4 Connect the red meter lead to the positive (+) terminal of a battery and the black meter lead to the negative (-) terminal of a battery. The meter reads the voltage difference between the leads.
  • DIGITAL METER USAGE 5 This jump start battery unit measures 13.151 volts with the meter set on autoranging on the DC voltage scale.
  • DIGITAL METER USAGE 6 Another meter (Fluke 87 III) displays four digits when measuring the voltage of the battery jump start unit.
  • DIGITAL METER USAGE 7 To measure resistance turn the rotary dial to the ohm (Ω) symbol. With the meter leads separated, the meter display reads OL (over limit).
  • DIGITAL METER USAGE 8 The meter can read your own body resistance if you grasp the meter lead terminals with your fingers. The reading on the display indicates 196.35 kΩ.
  • DIGITAL METER USAGE 9 When measuring anything; be sure to read the symbol on the meter face. In this case, the meter is reading 291.10 kΩ.
  • DIGITAL METER USAGE 10 A meter set on ohms can be used to check the resistance of a light bulb filament. In this case, the meter reads 3.15 ohms. If the bulb were bad (filament open), the meter would display OL.
  • DIGITAL METER USAGE 11 A digital meter set to read ohms should measure 0.00 as shown when the meter leads are touched together.
  • DIGITAL METER USAGE 12 The large letter V means volts and the wavy symbol over the V means that the meter measures alternating current (AC) voltage if this position is selected.
  • DIGITAL METER USAGE 13 The next symbol is a V with a dotted and a straight line overhead. This symbol stands for direct current (DC) volts. This position is most used for automotive service.
  • DIGITAL METER USAGE 14 The symbol mV indicates millivolts or 1/1000 of a volt (0.001). The solid and dashed line above the mV means DC mV.
  • DIGITAL METER USAGE 15 The rotary switch is turned to Ω (ohms) unit of resistance measure. The symbol to the left of the Ω symbol is the beeper or continuity indicator.
  • DIGITAL METER USAGE 16 Notice that AUTO is in the upper left and the MΩ is in the lower right. This MΩ means megaohms or that the meter is set to read in millions of ohms.
  • DIGITAL METER USAGE 17 The symbol shown is the symbol of a diode. In this position, the meter applies a voltage to a diode and the meter reads the voltage drop across the junction of a diode.
  • DIGITAL METER USAGE 18 One of the most useful features of this meter is the MIN/MAX feature. By pushing the MIN/MAX button, the meter will be able to display the highest (MAX) and the lowest (MIN) reading.
  • DIGITAL METER USAGE 19 Pushing the MIN/MAX button puts the meter into record mode. Note the 100 mS and “REC” on the display. In this position, the meter is capturing any voltage charge that lasts 100 mS (0.1 sec) or longer.
  • DIGITAL METER USAGE 20 To increase the range of the meter touch the range button. Now the meter is set to read voltage up to 40 volts DC.
  • DIGITAL METER USAGE 21 Pushing the range button one more time changes the meter scale to the 400-voltage range. Notice that the decimal point has moved to the right.
  • DIGITAL METER USAGE 22 Pushing the range button again changes the meter to the 4000-volt range. This range is not suitable to use in automotive applications.
  • DIGITAL METER USAGE 23 By pushing and holding the range button, the meter will reset to autorange. Autorange is the preferred setting for most automotive measurements except when using MIN/MAX record mode.

Halderman ch042 lecture Halderman ch042 lecture Presentation Transcript

  • CIRCUIT TESTERS AND DIGITAL METERS 42
  • Objectives
    • The student should be able to:
      • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis).
      • Discuss how to safely use a fused jumper wire, a test light, and a logic probe.
      • Explain how to set up and use a digital meter to read voltage, resistance, and current.
  • Objectives
    • The student should be able to:
      • Explain meter terms and readings.
      • Interpret meter readings and compare to factory specifications.
      • Discuss how to properly and safely use meters.
  • FUSED JUMPER WIRE
  • Fused Jumper Wire
    • Definition
      • Used to check circuit by bypassing switch or to provide power or ground to component
      • Can be purchased or made by service technician
  • Fused Jumper Wire
    • Definition
      • Blade-type fuse
      • Alligator clip ends
      • Good-quality insulated wire
  • Figure 42-1 A technician-made fused jumper lead, which is equipped with a red 10 ampere fuse. This fused jumper wire uses terminals for testing circuits at a connector instead of alligator clips.
  • Fused Jumper Wire
    • Uses of a Fused Jumper Wire
      • Help diagnose component or circuit by supplying temporary power and/or ground
      • If unit works, problem is in power side or ground side circuit
  • TEST LIGHTS
  • Test Lights
    • Nonpowered Test Light
      • Light bulb with a probe and a ground wire attached
      • Detects battery voltage potential at various test points
  • Figure 42-2 A 12 volt test light is attached to a good ground while probing for power.
  • Figure 42-3 A test light can be used to locate an open in a circuit. Note that the test light is grounded at a different location than the circuit itself.
  • Test Lights
    • Uses of a 12 Volt Test Light
      • Can be used to check electrical power and ground connection
      • Indicates only enough voltage and current to light test light (about 0.25 A)
  • Test Lights
    • Continuity Test Lights
      • Similar to test light but includes battery for self-power
      • Illuminates whenever connected to both ends of wire that has continuity
  • Test Lights
    • Continuity Test Lights
      • Not recommended for use with any electronic circuit; may harm delicate electronic components
  • Figure 42-4 A continuity light should not be used on computer circuits because the applied voltage can damage delicate electronic components or circuits.
  • Test Lights
    • High-Impedance Test Light
      • High internal resistance; draws very low current in order to light
      • Safe to use on computer circuits
  • Test Lights
    • High-Impedance Test Light
      • Some use electronic circuit to limit current flow, to avoid damage to electronic devices
      • LED test light uses LED instead for visual indication of voltage
        • Requires about 25 milliamperes (0.025 ampere) to light
  • Test Lights
    • High-Impedance Test Light
      • Some use electronic circuit to limit current flow, to avoid damage to electronic devices
      • LED test light uses LED instead for visual indication of voltage
        • Can be used on electronic circuits as well as standard circuits
  • Figure 42-5 An LED test light can be easily made using low cost components and an old ink pen. With the 470 ohm resistor in series with the LED, this tester only draws 0.025 ampere (25 milliamperes) from the circuit being tested. This low current draw helps assure the technician that the circuit or component being tested will not be damaged by excessive current flow.
  • LOGIC PROBE
  • Logic Probe
    • Purpose and Function
      • Lights up red (usually) LED if probe touched to battery voltage
      • Lights up green (usually) LED if probe touched to ground
  • Logic Probe
    • Purpose and Function
      • Can “sense” difference between high- and low-voltage levels
        • Can also light another light (often amber) when change in voltage occurs
  • Logic Probe
    • Purpose and Function
      • Can “sense” difference between high- and low-voltage levels
        • Some flash red light when pulsing voltage signal detected
  • Logic Probe
    • Purpose and Function
      • Can “sense” difference between high- and low-voltage levels
        • Some flash green light when pulsing ground signal detected
  • Logic Probe
    • Purpose and Function
      • Can “sense” difference between high- and low-voltage levels
        • Helpful when checking for variable voltage output from computer or ignition sensor
  • Figure 42-6 A logic probe connected to the vehicle battery. When the tip probe is connected to a circuit, it can check for power, ground, or a pulse.
  • Logic Probe
    • Using a Logic Probe
      • Must first be connected to power and ground source (vehicle battery)
        • Powers probe and gives it reference low (ground)
  • Logic Probe
    • Using a Logic Probe
      • Also makes distinctive sound for each high- and low-voltage level
      • Makes troubleshooting easier when probing connectors or component terminals
  • Logic Probe
    • Using a Logic Probe
      • Can be used to check components such as:
        • Pickup coils
        • Hall-effect sensors
        • Magnetic sensors
  • DIGITAL MULTIMETERS
  • Digital Multimeters
    • Terminology
      • Digital multimeter (DMM), digital volt-ohm-meter (DVOM) common names for electronic high-impedance test meters
  • Digital Multimeters
    • Terminology
      • High impedance means electronic internal resistance of meter high enough to prevent excessive current draw from circuit being tested
  • Digital Multimeters
    • Terminology
      • Required for measuring computer circuits
      • Can be used to measure any automotive circuit within ranges of meter
  • Figure 42-7 Typical digital multimeter. The black meter lead always is placed in the COM terminal. The red meter test lead should be in the volt-ohm terminal except when measuring current in amperes.
  • Chart 42-1 Common symbols and abbreviations used on digital meters.
  • Digital Multimeters
    • Measuring Voltage
      • Voltmeter measures pressure or potential of electricity in volts
      • Voltmeter connected to circuit in parallel
  • Digital Multimeters
    • Measuring Voltage
      • Voltage can be measured by selecting either AC or DC volts
        • DC volts (DCV): Most common setting for automotive use
          • Battery voltage, voltage to lighting and accessory circuits
  • Digital Multimeters
    • Measuring Voltage
      • Voltage can be measured by selecting either AC or DC volts
        • AC volts (ACV): Check for unwanted AC voltage from alternators and some sensors
  • Digital Multimeters
    • Measuring Voltage
      • Voltage can be measured by selecting either AC or DC volts
        • Range: Automatically set for most meters; can be manually ranged
  • Figure 42-8 Typical digital multimeter (DMM) set to read DC volts.
  • Figure 42-9 (a) A typical autoranging digital multimeter automatically selects the proper scale to read the voltage being tested. The scale selected is usually displayed on the meter face. Note that the display indicates “4,” meaning that this range can read up to 4 volts.
  • Figure 42-9 (b) A typical autoranging digital multimeter automatically selects the proper scale to read the voltage being tested. The scale selected is usually displayed on the meter face.The range is now set to the 40 volt scale, meaning that the meter can read up to 40 volts on the scale. Any reading above this level will cause the meter to reset to a higher scale. If not set on autoranging, the meter display would indicate OL if a reading exceeds the limit of the scale selected.
  • Digital Multimeters
    • Measuring Resistance
      • Ohmmeter measures resistance of component or circuit section when no current flowing through
      • Connected in series with component or wire being measured
  • Digital Multimeters
    • Measuring Resistance
      • When connected to component, current flows through leads and voltage drop between leads measured as resistance
  • Digital Multimeters
    • Measuring Resistance
      • Zero ohms means no resistance between test leads
        • Indicates continuity for current to flow in closed circuit
  • Digital Multimeters
    • Measuring Resistance
      • Infinity means no connection, or open circuit
      • Ohmmeters have no required polarity even though red and black test leads are used
  • Digital Multimeters
    • Measuring Resistance
      • CAUTION: Circuit must be electrically open with no current flowing when using ohmmeter.
  • Digital Multimeters
    • Measuring Resistance
      • Meters have different ways of indicating infinity resistance, or reading higher than scale allows
        • OL, meaning over limit or overload
  • Digital Multimeters
    • Measuring Resistance
      • Meters have different ways of indicating infinity resistance, or reading higher than scale allows
        • Flashing or solid number 1
  • Digital Multimeters
    • Measuring Resistance
      • Meters have different ways of indicating infinity resistance, or reading higher than scale allows
        • Flashing or solid number 3 on the left side of the display
  • Digital Multimeters
    • Measuring Resistance
      • Meters have different ways of indicating infinity resistance, or reading higher than scale allows
        • Flashing or solid number 4 on the display
    ?
  • Figure 42-10 Using a digital multimeter set to read ohms (Ω) to test this light bulb. The meter reads the resistance of the filament.
  • Figure 42-11 Many digital multimeters can have the display indicate zero to compensate for test lead resistance. (1) Connect leads in the V Ω and COM meter terminals. (2) Select the Ω scale. (3) Touch the two meter leads together. (4) Push the “zero” or “relative” button on the meter. (5) The meter display will now indicate zero ohms of resistance.
  • Digital Multimeters
    • Measuring Amperes
      • Ammeter measures flow of current through complete circuit in amperes
      • Ammeter has to be installed in circuit (in series) so it can measure all current flow in circuit
    ?
  • Figure 42-12 Measuring the current flow required by a horn requires that the ammeter be connected to the circuit in series and the horn button be depressed by an assistant.
  • INDUCTIVE AMMETERS
  • Inductive Ammeters
    • Operation
      • Do not make physical contact with circuit
      • Measure strength of magnetic field surrounding wire carrying current
  • Inductive Ammeters
    • Operation
      • Use Hall-effect sensor to measure current
      • Sensor detects strength of magnetic field surrounding wire carrying current
  • Figure 42-14 An inductive ammeter clamp is used with all starting and charging testers to measure the current flow through the battery cables.
  • Inductive Ammeters
    • AC/DC Clamp-On Digital Multimeters
      • Advantage: No need to break circuit to measure current (amperes)
      • Simply clamp jaws of meter around power lead(s) or ground lead(s) of component being measured and read display
  • Inductive Ammeters
    • AC/DC Clamp-On Digital Multimeters
      • Can also measure AC, which helps diagnose alternator problem
      • Volts, ohms, frequency, temperature can also be measured
  • Figure 42-15 A typical mini clamp-on-type digital multimeter. This meter is capable of measuring alternating current (AC) and direct current (DC) without requiring that the circuit be disconnected to install the meter in series. The jaws are simply placed over the wire and current flow through the circuit is displayed.
  • DIODE CHECK, PULSE WIDTH, AND FREQUENCY
  • Diode Check, Pulse Width, and Frequency
    • Diode Check
      • Meter applies 3 volt DC signal to test leads
      • Voltage high enough to cause diode to work and meter to display
        • 0.4–0.7 volt when testing silicon diodes as in alternators
  • Diode Check, Pulse Width, and Frequency
    • Diode Check
      • Voltage high enough to cause diode to work and meter to display
        • 2. 1.5–2.3 volts when testing LEDs as in some lighting applications
  • Diode Check, Pulse Width, and Frequency
    • Pulse Width
      • 100% pulse width indicates device being commanded on all the time
      • 50% indicates device being commanded on half the time
  • Diode Check, Pulse Width, and Frequency
    • Pulse Width
      • 25% indicates device being commanded on just 25% of time
      • Measures on time for fuel injectors, other computer-controlled devices
  • Diode Check Pulse Width and Frequency
    • Frequency
      • Measure of how many times per second signal changes
      • Used when checking:
        • Mass airflow (MAF) sensors for proper operation
    Diode Check, Pulse Width, and Frequency
  • Diode Check, Pulse Width, and Frequency
    • Frequency
      • Used when checking:
        • Ignition primary pulse signals when diagnosing no-start condition
  • Diode Check, Pulse Width, and Frequency
    • Frequency
      • Used when checking:
        • Checking wheel speed sensor
  • ELECTRICAL UNIT PREFIXES
  • Electrical Unit Prefixes
    • Definitions
      • Kilo (k) means 1,000
        • 4,700 ohms = 4.7 kilohms (kΩ)
  • Electrical Unit Prefixes
    • Definitions
      • Mega (M) means 1 million
        • 1,100,000 volts = 1.1 megavolts (MV)
        • 4,700,000 ohms = 4.7 megohms (MΩ)
  • Electrical Unit Prefixes
    • Definitions
      • milli (m) means 1/1,000
      • HINT: Lowercase m is small unit (milli); capital M is large unit (mega).
  • Figure 42-17 Always look at the meter display when a measurement is being made, especially if using an autoranging meter.
  • Chart 42-2 A conversion chart showing the decimal point location for the various prefixes.
  • Electrical Unit Prefixes
    • Prefixes
      • Most digital meters can express values in more than one unit
      • Ammeter may show 36.7 mA on autoranging
      • When scale changed to amperes number displayed will be 0.037 A
  • HOW TO READ DIGITAL METERS
  • How to Read Digital Meters
    • Steps to Follow
      • Select proper unit of electricity for what is being measured
      • Place meter leads into proper input terminals
  • How to Read Digital Meters
    • Steps to Follow
      • Measure component being tested
      • Interpret reading
  • Chart 42-3 Sample meter readings using manually set and autoranging selection on the digital meter control.
  • Chart 42-3 (continued) Sample meter readings using manually set and autoranging selection on the digital meter control.
  • How to Read Digital Meters
    • RMS Versus Average
      • AC voltage waveforms can be true sinusoidal or nonsinusoidal
      • True sine wave pattern measurement will be same for both root-mean-square (RMS) and average reading meters
  • Figure 42-18 When reading AC voltage signals, a true RMS meter (such as a Fluke 87) provides a different reading than an average responding meter (such as a Fluke 88). The only place this difference is important is when a reading is to be compared with a specification.
  • How to Read Digital Meters
    • Resolution, Digits, and Counts
      • Meter resolution: how small or fine a measurement meter can make
        • Resolution tells whether DMM can measure down to 1 volt or to 1 millivolt
  • How to Read Digital Meters
    • Resolution, Digits, and Counts
      • Digits and counts describe meter’s resolution
        • DMMs grouped by number of counts or digits they display
  • How to Read Digital Meters
    • Resolution, Digits, and Counts
      • 3 1/2-digit meter can display three full digits from 0 to 9, and one “half” digit (only a 1 or blank)
        • Will display up to 1,999 counts of resolution
  • How to Read Digital Meters
    • Resolution, Digits, and Counts
      • 4 1/2-digit meter can display up to 19,000 counts of resolution
  • Figure 42-19 This meter display shows 052.2 AC volts. Notice that the zero beside the 5 indicates that the meter can read over 100 volts AC with a resolution of 0.1 volt.
  • How to Read Digital Meters
    • Accuracy
      • Largest allowable error that will occur under specific operating conditions
      • Accuracy usually expressed as percent of reading
  • How to Read Digital Meters
    • Accuracy
      • Accuracy of +/-1% means that for displayed reading of 100.0 V, actual value could be between 99.0 V and 101.0 V
  • How to Read Digital Meters
    • Accuracy
      • The lower the percent of accuracy, the better
        • Unacceptable = 1.00%
        • Okay = 0.50% (1/2%)
  • How to Read Digital Meters
    • Accuracy
      • The lower the percent of accuracy, the better
        • Good = 0.25% (1/4%)
        • Excellent = 0.10% (1/10%)
  • DIGITAL METER USAGE 1 For most electrical measurements, the black meter lead is inserted in the terminal labeled COM and the red meter lead is inserted into the terminal labeled V.
  • DIGITAL METER USAGE 2 To use a digital meter, turn the power switch and select the unit of electricity to be measured. In this case, the rotary switch is turned to select DC volts. (V)
  • DIGITAL METER USAGE 3 For most automotive electrical use, such as measuring battery voltage, select DC volts.
  • DIGITAL METER USAGE 4 Connect the red meter lead to the positive (+) terminal of a battery and the black meter lead to the negative (-) terminal of a battery. The meter reads the voltage difference between the leads.
  • DIGITAL METER USAGE 5 This jump start battery unit measures 13.151 volts with the meter set on autoranging on the DC voltage scale.
  • DIGITAL METER USAGE 6 Another meter (Fluke 87 III) displays four digits when measuring the voltage of the battery jump start unit.
  • DIGITAL METER USAGE 7 To measure resistance turn the rotary dial to the ohm (Ω) symbol. With the meter leads separated, the meter display reads OL (over limit).
  • DIGITAL METER USAGE 8 The meter can read your own body resistance if you grasp the meter lead terminals with your fingers. The reading on the display indicates 196.35 kΩ.
  • DIGITAL METER USAGE 9 When measuring anything; be sure to read the symbol on the meter face. In this case, the meter is reading 291.10 kΩ.
  • DIGITAL METER USAGE 10 A meter set on ohms can be used to check the resistance of a light bulb filament. In this case, the meter reads 3.15 ohms. If the bulb were bad (filament open), the meter would display OL.
  • DIGITAL METER USAGE 11 A digital meter set to read ohms should measure 0.00 as shown when the meter leads are touched together.
  • DIGITAL METER USAGE 12 The large letter V means volts and the wavy symbol over the V means that the meter measures alternating current (AC) voltage if this position is selected.
  • DIGITAL METER USAGE 13 The next symbol is a V with a dotted and a straight line overhead. This symbol stands for direct current (DC) volts. This position is most used for automotive service.
  • DIGITAL METER USAGE 14 The symbol mV indicates millivolts or 1/1000 of a volt (0.001). The solid and dashed line above the mV means DC mV.
  • DIGITAL METER USAGE 15 The rotary switch is turned to Ω (ohms) unit of resistance measure. The symbol to the left of the Ω symbol is the beeper or continuity indicator.
  • DIGITAL METER USAGE 16 Notice that AUTO is in the upper left and the MΩ is in the lower right. This MΩ means megaohms or that the meter is set to read in millions of ohms.
  • DIGITAL METER USAGE 17 The symbol shown is the symbol of a diode. In this position, the meter applies a voltage to a diode and the meter reads the voltage drop across the junction of a diode.
  • DIGITAL METER USAGE 18 One of the most useful features of this meter is the MIN/MAX feature. By pushing the MIN/MAX button, the meter will be able to display the highest (MAX) and the lowest (MIN) reading.
  • DIGITAL METER USAGE 19 Pushing the MIN/MAX button puts the meter into record mode. Note the 100 mS and “REC” on the display. In this position, the meter is capturing any voltage charge that lasts 100 mS (0.1 sec) or longer.
  • DIGITAL METER USAGE 20 To increase the range of the meter touch the range button. Now the meter is set to read voltage up to 40 volts DC.
  • DIGITAL METER USAGE 21 Pushing the range button one more time changes the meter scale to the 400-voltage range. Notice that the decimal point has moved to the right.
  • DIGITAL METER USAGE 22 Pushing the range button again changes the meter to the 4000-volt range. This range is not suitable to use in automotive applications.
  • DIGITAL METER USAGE 23 By pushing and holding the range button, the meter will reset to autorange. Autorange is the preferred setting for most automotive measurements except when using MIN/MAX record mode.
  • FREQUENTLY ASKED QUESTION
    • How Much Voltage Does an Ohmmeter Apply?
      • Most digital meters that are set to measure ohms (resistance) apply 0.3 to 1 volt to the component being measured. The voltage comes from the meter itself to measure the resistance. Two things are important to remember about an ohmmeter.
    ? BACK TO PRESENTATION 1. The component or circuit must be disconnected from any electrical circuit while the resistance is being measured. 2. Because the meter itself applies a voltage (even though it is relatively low), a meter set to measure ohms can damage electronic circuits. Computer or electronic chips can be easily damaged if subjected to only a few milliamperes of current, similar to the amount an ohmmeter applies when a resistance measurement is being performed.
  • TECH TIP
    • Fuse Your Meter Leads!
      • Most digital meters include an ammeter capability. When reading amperes, the leads of the meter must be changed from volts or ohms (V or Ω) to amperes (A), milliamperes (mA), or microamperes (μA).
    BACK TO PRESENTATION
    • A common problem may then occur the next time voltage is measured. Although the technician may switch the selector to read volts, often the leads are not switched back to the volt or ohm position. Because the ammeter lead position results in zero ohms of resistance to current flow through the meter, the meter or the fuse inside the meter will be destroyed if the meter is connected to a battery. Many meter fuses are expensive and difficult to find.
    • To avoid this problem, simply solder an inline 10 ampere blade-fuse holder into one meter lead.
    • Do not think that this technique is for beginners only. Experienced technicians often get in a hurry and forget to switch the lead. A blade fuse is faster, easier, and less expensive to replace than a meter fuse or the meter itself. Also, if the soldering is done properly, the addition of an inline fuse holder and fuse does not increase the resistance of the meter leads. All meter leads have some resistance.
    • If the meter is measuring very low resistance, touch the two leads together and read the resistance (usually no more than 0.2 ohm). Simply subtract the resistance of the leads from the resistance of the component being measured.
      • Figure 42-13 Note the blade-type fuse holder soldered in series with one of the meter leads. A 10 ampere fuse helps protect the internal meter fuse (if equipped) and the meter itself from damage that may result from excessive current flow if accidentally used incorrectly.
  • FREQUENTLY ASKED QUESTION
    • What Does “CE” Mean on Many Meters?
      • The “CE” means that the meter meets the newest European Standards and the letters CE stands for a French term for “Conformité Europeenne” meaning European Conformity in French.
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  • TECH TIP
    • Over Limit Display Does Not Mean the Meter Is Reading “Nothing”
      • The meaning of the over limit display on a digital meter often confuses beginning technicians. When asked what the meter is reading when an over limit (OL) is displayed on the meter face, the response is often, “Nothing.”
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    • Many meters indicate over limit or over load, which simply means that the reading is over the maximum that can be displayed for the selected range. For example, the meter will display OL if 12 volts are being measured but the meter has been set to read a maximum of 4 volts.
    • Autoranging meters adjust the range to match what is being measured. Here OL means a value higher than the meter can read (unlikely on the voltage scale for automobile usage), or infinity when measuring resistance (ohms). Therefore, OL means infinity when measuring resistance or an open circuit is being indicated.
    • The meter will read 00.0 if the resistance is zero, so “nothing” in this case indicates continuity (zero resistance), whereas OL indicates infinity resistance. Therefore, when talking with another technician about a meter reading, make sure you know exactly what the reading on the face of the meter means. Also be sure that you are connecting the meter leads correctly.
      • Figure 42-16 Typical digital multimeter showing OL (over limit) on the readout with the ohms (Ω) unit selected. This usually means that the unit being measured is open (infinity resistance) and has no continuity.
  • TECH TIP
    • Think of Money
      • Digital meter displays can often be confusing. The display for a battery measured as 12 1/2 volts would be 12.50 V, just as $12.50 is 12 dollars and 50 cents. A 1/2 volt reading on a digital meter will be displayed as 0.50 V, just as $0.50 is half of a dollar.
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    • It is more confusing when low values are displayed. For example, if a voltage reading is 0.063 volt, an autoranging meter will display 63 millivolts (63 mV), or 63/1,000 of a volt, or $63 of $1,000. (It takes 1,000 mV to equal 1 volt.) Think of millivolts as one-tenth of a cent, with 1 volt being $1.00. Therefore, 630 millivolts are equal to $0.63 of $1.00 (630 tenths of a cent, or 63 cents).
    • To avoid confusion, try to manually range the meter to read base units (whole volts). If the meter is ranged to base unit volts, 63 millivolts would be displayed as 0.063 or maybe just 0.06, depending on the display capabilities of the meter.
  • TECH TIP
    • Purchase a Digital Meter That Will Work for Automotive Use
      • Try to purchase a digital meter that is capable of reading the following:
        • DC volts
        • AC volts
        • DC amperes (up to 10 A or more is helpful)
        • Ohms (Ω) up to 40 MΩ (40 million ohms)
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    • Try to purchase a digital meter that is capable of reading the following:
      • Diode check
    • Additional features for advanced automotive diagnosis include:
      • Frequency (hertz, abbreviated Hz)
      • Temperature probe (°F and/or °C)
      • Pulse width (millisecond, abbreviated ms)
      • Duty cycle (%)
  • SAFETY TIP
    • Meter Usage on Hybrid Electric Vehicles
      • Many hybrid electric vehicles use system voltage as high as 650 volts DC. Be sure to follow all vehicle manufacturer’s testing procedures; and if a voltage measurement is needed, be sure to use a meter and test leads that are designed to insulate against high voltages.
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      • The International Electrotechnical Commission (IEC) has several categories of voltage standards for meter and meter leads. These categories are ratings for overvoltage protection and are rated CAT I, CAT II, CAT III, and CAT IV. The higher the category, the greater the protection against voltage spikes caused by high-energy circuits. Under each category there are various energy and voltage ratings.
      • CAT I: Typically a CAT I meter is used for low-energy voltage measurements such as at wall outlets in the home. Meters with a CAT I rating are usually rated at 300 to 800 volts.
      • CAT II: This higher rated meter would be typically used for checking higher energy level voltages at the fuse panel in the home. Meters with a CAT II rating are usually rated at 300 to 600 volts.
      • CAT III: This minimum rated meter should be used for hybrid vehicles. The CAT III category is designed for high-energy levels and voltage measurements at the service pole at the transformer. Meters with this rating are usually rated at 600 to 1,000 volts.
      • CAT IV: CAT IV meters are for clamp-on meters only. If a clamp-on meter also has meter leads for voltage measurements, that part of the meter will be rated as CAT III.
      • NOTE: Always use the highest CAT rating meter, especially when working with hybrid vehicles. A CAT III, 600 volt meter is safer than a CAT II, 1,000 volt meter because of the energy level of the CAT ratings.
      • Therefore, for best personal protection, use only meters and meter leads that are CAT III or CAT IV rated when measuring voltage on a hybrid vehicle.
      • Figure 42-20 Be sure to only use a meter that is CAT III rated when taking electrical voltage measurements on a hybrid vehicle.
      • Figure 42-21 Always use meter leads that are CAT III rated on a meter that is also CAT III rated, to maintain the protection needed when working on hybrid vehicles.