At 43 ch 9 digital meters

Automotive Fuel and Emissions Control Systems, 2/eBy James D. Halderman and Jim Linder

© 2009 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

TEST LIGHTS

• A test light is one of the simplest testers that can be used to detect electricity.

• A test light is simply a light bulb with a probe and a ground wire attached.

FIGURE 9-1 A 12-volt test light is attached to a good ground while probing for power.



TEST LIGHTS

FIGURE 9-2 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 LIGHTSContinuity Test Lights

• A continuity light is similar to a test light but includes a battery for self-power.

• A continuity light illuminates whenever it is connected to both ends of a wire that has continuity or is not broken.

FIGURE 9-3 Self-powered test lights contain a battery, clamp, and probe. This type of test light should not be used on any computer-controlled circuits because the applied voltage can damage delicate electronic components or circuits.



TEST LIGHTSLED Test Light

• An LED test light uses an LED instead of a standard automotive bulb for a visual indication of voltage.

FIGURE 9-4 High-impedance test light. 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.



TEST LIGHTSLogic Probe

• A logic probe is an electronic device that lights up a red (usually) LED if the probe is touched to battery voltage.

FIGURE 9-5 A logic probe connected to the vehicle battery and relay used to check for power, ground, or a pulse.



DIGITAL MULTIMETERS

• Digital multimeter (DMM) and digital volt-ohmmilliammeter (DVOM) are terms commonly used for electronic high-impedance test meters.

• High-impedance meters, required for measuring computer circuits, are digital meters; however, not all digital meters have the required 10 megohms (M) (10 million ohms) of internal resistance.



DIGITAL MULTIMETERS

FIGURE 9-6 Typical digital multimeter. The black meter lead always is placed in the COM terminal. Except when measuring the current in amperes, the red meter test lead remains in the V terminal.



DIGITAL MULTIMETERS

FIGURE 9-7 Common abbreviations used on the display face of many digital multimeters. (Courtesy of Fluke Corporation)



DIGITAL MULTIMETERS

FIGURE 9-8 A summary chart indicating what measurement type may be used to test which vehicle system.(Courtesy of Fluke Corporation)



DIGITAL MULTIMETERSMeasuring Voltage

• A voltmeter measures the pressure or potential of electricity in units of volts.

FIGURE 9-9 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. (a) Note that the display indicates “4,” meaning that this range can read up to 4 volts. (b) 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. (Courtesy of Fluke Corporation)



DIGITAL MULTIMETERSMeasuring Voltage

FIGURE 9-10 Typical digital multimeter (DMM) set to read DC volts.



DIGITAL MULTIMETERSMeasuring Resistance

• An ohmmeter measures the resistance in ohms of a component or circuit section when no current is flowing through the circuit.

• An ohmmeter contains a battery (or other power source). – When the leads are connected to a component, current flows through

the test leads and the difference in voltage (voltage drop) between the leads is measured as resistance.

• Zero ohms on the scale means no resistance between the test leads, indicating that there is continuity or a continuous path for the current to flow in a closed circuit. – Infinity means no connection, as in an open circuit.




FIGURE 9-11 Using a digital multimeter set to read ohms () to test this light bulb. The meter reads the resistance of the filament.




FIGURE 9-12 Typical digital multimeter showing OL (over limit) on the readout with the ohms () unit selected. This usually means that the unit being measured is open (infinity resistance) and has no continuity.




FIGURE 9-13 Many digital multimeters can have the display indicate zero to compensate for test lead resistance. (1) Connect leads in the VΩ 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. (Courtesy of Fluke Corporation)



DIGITAL MULTIMETERSMeasuring Amperes

FIGURE 9-14 In this digital multimeter set to read DC amperes, note that the red lead is placed in the far left-hand socket of the meter. The meter is displaying the current flow (4.18 A) through the electric fuel pump on this General Motors 3800 V6 engine.



DIGITAL MULTIMETERSMeasuring Amperes

• An ammeter measures the flow of current through a complete circuit in units of amperes.

• The ammeter has to be installed in the circuit (in series) so that it can measure all the current flow in that circuit.

FIGURE 9-15 An inductive ammeter clamp is used with all starting and charging testers to measure the current flow through the battery cables.



AC/DC CLAMP-ON DIGITAL MULTIMETER

• An AC/DC clamp-on digital multimeter (DMM) is a useful meter for automotive diagnostic work and uses a Hall-effect sensor to measure current.

FIGURE 9-16 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.



AC/DC CLAMP-ON DIGITAL MULTIMETER

FIGURE 9-17 An AC and DC current clamp such as the one shown can be used with a regular digital multimeter. The amp probe contains a separate battery and electronic circuit that converts the amperage reading into a millivolt (mV) signal.



FUSE YOUR METER LEADS!

FIGURE 9-18 Note the blade-type fuse holder soldered in series with one of the meter leads. A 10 amp fuse helps protect the internal meter fuse (if equipped) and the meter itself from damage that might result from excessive current flow if accidentally used incorrectly.



“OL” DOES NOT MEAN THE METER IS READING “NOTHING”

FIGURE 9-19 A summary of the test meter hookup.



ELECTRICAL UNIT PREFIXES

• Electrical units are measured in numbers such as 12-volts, 150 amperes, and 470 ohms.

• Large units over 1,000 may be expressed in kilo units.

• Kilo (k) means 1,000.

FIGURE 9-20 Always look at the meter display when a measurement is being made,especially if using an autoranging meter.(Courtesy of Fluke Corporation)



HOW TO READ DIGITAL METERS

• Getting to know and use a digital meter takes time and practice.

• The first step is to read, understand, and follow all safety and operational instructions that come with the meter.

• Use of the meter usually involves the following steps.– Select the proper unit of electricity for what is being

measured.– Place the meter leads into the proper input terminals.– Measure the component being tested.– Interpret the reading.



METER USAGE ON HYBRID ELECTRIC VEHICLES

FIGURE 9-24 Be sure to only use a meter that is CAT III rated when taking electrical voltage measurements on a hybrid vehicle.



METER USAGE ON HYBRID ELECTRIC VEHICLES

FIGURE 9-25 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.

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At 43 ch 9 digital meters