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Transcript
PowerPoint® Presentation Chapter 9 Taking Standard Measurements Taking Measurements • Voltage • Voltage Indicators • DC Voltage Measurement • Current • Resistance • Temperature • Speed • Scopes • Scopemeters • Manually-Operated Controls • Digital Logic Probes Chapter 9 — Taking Standard Measurements A test light is a test instrument with a bulb that is connected to two test leads to give a visual indication when voltage is present in a circuit. Chapter 9 — Taking Standard Measurements When testing a receptacle, the test light bulb illuminates when the receptacle is properly wired and energized. Chapter 9 — Taking Standard Measurements A receptacle tester is a device that is plugged into a standard receptacle to determine if the receptacle is properly wired and energized. Chapter 9 — Taking Standard Measurements Refer to the operating manual of the test instrument for all measuring precautions limitations, and procedures. Chapter 9 — Taking Standard Measurements A voltage indicator is a test instrument that indicates the presence of voltage when the test tip touches, or is near, an energized hot conductor or energized metal part. Chapter 9 — Taking Standard Measurements Always follow a voltage indicator test with a test using a voltmeter to verify the voltage indicator measurement any time the voltage indicator indicates no voltage. Chapter 9 — Taking Standard Measurements A voltage tester is an electrical test instrument that indicates the approximate voltage amount and type of voltage (AC or DC) in a circuit by the movement of a pointer (and vibration on some models). Chapter 9 — Taking Standard Measurements Before taking any voltage measurements using a voltage tester, ensure the tester is designed to take measurements on the circuit being tested. Chapter 9 — Taking Standard Measurements Exercise caution when measuring AC voltages over 24 V. Chapter 9 — Taking Standard Measurements Exercise caution when measuring DC voltages over 60 V. Chapter 9 — Taking Standard Measurements Care must be taken to protect the meter, circuit, and person using the meter when measuring DC with an in-line ammeter. Chapter 9 — Taking Standard Measurements Clamp-on ammeters measure the current in a circuit by measuring the strength of the magnetic field around a conductor. Chapter 9 — Taking Standard Measurements An ohmmeter measures resistance with all power to the circuit OFF. Chapter 9 — Taking Standard Measurements A megohmmeter detects insulation failure or potential failure of insulation caused by excessive moisture, dirt, heat, cold, corrosive substances, vibration, and aging. Chapter 9 — Taking Standard Measurements The amount of temperature at a location can be measured using a contact thermometer or infrared meter. Chapter 9 — Taking Standard Measurements A contact thermometer is an instrument that measures temperature at a single point. Chapter 9 — Taking Standard Measurements An infrared meter is a meter that measures heat energy by measuring the infrared energy that a material emits. Chapter 9 — Taking Standard Measurements The speed of a rotating object can be measured using a contact tachometer, photo tachometer, or strobe tachometer. Chapter 9 — Taking Standard Measurements A contact tachometer is a device that measures the rotational speed of an object through direct contact of the tachometer tip with the object to be measured Chapter 9 — Taking Standard Measurements A photo tachometer is a device that measures the speed of an object without direct contact with the object. Chapter 9 — Taking Standard Measurements A strobe tachometer is a device that uses a flashing light to measure the speed of a moving object. Chapter 9 — Taking Standard Measurements The two basic types of scopes used in troubleshooting are oscilloscopes and scopemeters. Chapter 9 — Taking Standard Measurements A scope displays the voltage under test on the scope screen. Chapter 9 — Taking Standard Measurements A trace is a reference point/line that is visually displayed on the face of the scope screen. Chapter 9 — Taking Standard Measurements Typical manually-operated scope adjustment controls include intensity, focus, horizontal positioning, vertical positioning, volts/division, and time/division. Chapter 9 — Taking Standard Measurements The volts/division (volts per division) control selects the height of the displayed waveform. Chapter 9 — Taking Standard Measurements The time/division (time per division) control selects the width of the displayed waveform. Chapter 9 — Taking Standard Measurements A scope is connected by a probe on the end of a test lead. A 1X probe (1 to 1) is used to connect the input of the scope to the circuit under test when the test voltage is lower than the voltage limit of the scope. Chapter 9 — Taking Standard Measurements A scopemeter gives an adequate reading in most frequency measurement applications. Chapter 9 — Taking Standard Measurements To measure AC voltage using a scope, a test probe is connected to the point in the circuit where the DC voltage is to be measured. Chapter 9 — Taking Standard Measurements A digital logic probe is a special DC voltmeter that detects the presence or absence of a signal. Chapter 9 — Taking Standard Measurements A power supply voltage is checked with voltmeter if the digital circuit or logic probe has intermittent problems.