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BRANCH-E&TC ENGINEERING

SEM – 3Rd

SUBJECT-EMI

CHAPTER-02- indicating instrument

TOPIC- ohm meter

Ay-2021-2022 ,winter-2021

FACULTY-ER V BEHERA.(LECTURER e & tc engg Dept)

Presentation On

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OHM METER

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OBJECTIVES

  • After completing this chapter, you will be able to:
    • Identify the two types of meter movements available
    • Describe how a voltmeter is used in a circuit
    • Describe how an ammeter is used in a circuit
    • Describe how an ohmmeter is used for measuring resistance

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OBJECTIVES (CONT’D.)

    • Identify the functions of a multimeter
    • Identify the advantages/disadvantages of DMMs and VOMs
    • Describe how to use a multimeter to measure voltage, current, and resistance
    • Describe how to measure current using an ammeter
    • Describe how to connect an ammeter into a circuit

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OBJECTIVES (CONT’D.)

    • List safety precautions for using an ammeter
    • Describe how to connect a voltmeter to an electrical circuit
    • List safety precautions for connecting a voltmeter to a circuit
    • Describe how resistance values are measured using an ohmmeter
    • Define continuity check

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OBJECTIVES (CONT’D.)

    • Describe how an ohmmeter is used to check open, short, or closed circuits

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INTRODUCTION TO METERS

  • Analog meter
    • Uses a graduated scale with a pointer
  • Digital meter
    • Provides a reading in numbers
    • More accurate than analog meters

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TYPES OF METERS

Figure 6-5. The placement of an ammeter in a circuit.

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TYPES OF METERS (CONT’D.)

Figure 6-6. (A) Schematic symbol for a voltmeter.

(B) A voltmeter is connected in parallel in a circuit.

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TYPES OF METERS (CONT’D.)

Figure 6-7. (A) Schematic symbol for an ohmmeter. (B) An ohmmeter applies

a voltage across the component being measured and monitors the current

flowing through it.

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MULTIMETERS

  • Multimeter
    • Combines a voltmeter, ammeter, and ohmmeter into one package
  • VOM (volt-ohm-milliammeter)
    • An analog multimeter that measures volts, ohms, and milliamperes
  • DMM
    • A digital multimeter

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Figure 6-8. An analog multimeter.

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MULTIMETERS (CONT’D.)

  • Advantages of DMMs over VOMs:
    • Easier readability, resulting in a higher accuracy with smaller voltage
    • Autoranging capabilities
    • Autozeroing for resistance reading
    • Autolock of a displayed value

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MULTIMETERS (CONT’D.)

  • Disadvantages of a DMM:
    • Requirement for source of electricity
    • Voltage limitation
    • Inability to measure an instantaneous change in a signal faster than the sampling time

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MEASURING CURRENT�

Figure 6-9. An ammeter is connected in series to a circuit.

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Figure 6-10. An ammeter is one part of this VOM. A black negative lead plugs into the

common or negative hack. A red positive lead plugs into the jack with the plus symbol.

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MEASURING CURRENT (CONT’D.)�

  • Caution:
    • Always turn off power before connecting an ammeter to a circuit
    • An analog ammeter must never be connected in parallel
    • Never connect an ammeter directly to a voltage source

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MEASURING VOLTAGE

Figure 6-13. When connecting a voltmeter into a circuit, be sure to observe polarity.

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MEASURING VOLTAGE (CONT’D.)

  • Caution:
    • If an analog voltmeter is connected in series with a circuit, a large current can flow through the meter and might damage it

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MEASURING RESISTANCE

Figure 6-14. When using an ohmmeter to measure resistance, the component being measured must be removed from the circuit.

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MEASURING RESISTANCE (CONT’D.)

  • Continuity test (or check)
    • Determines if current path is continuous
    • Open circuit
      • Indicates high resistance
    • Short circuit
      • Zero ohms of resistance
    • Closed circuit
      • Indicates low resistance

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READING METER SCALES�

  • Full scale value
    • Maximum value indicated by a meter
  • Ammeters and voltmeters
    • Read from left to right
    • Linear scales
  • Ohmmeters
    • Read from right to left
    • Nonlinear scales

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SUMMARY

  • Analog meters use a graduated scale with a pointer
  • Digital meters provide a direct readout
  • A multimeter combines a voltmeter, ammeter, and ohmmeter into one package
  • A VOM is an analog multimeter
  • A DMM is a digital multimeter

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SUMMARY

  • On a multimeter, the range selector switch selects the function to be used
  • An ammeter must be connected in series with a circuit
  • A voltmeter is connected in parallel with a circuit
  • An ohmmeter measures resistance by applying a known voltage

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Thank You