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Chapter 10

Chapter 10. Measuring Frequency and Duty Cycle. Frequency • Frequency Measurement • Frequency Measurement Procedures • Measuring Frequency with Clamp-On Meter • Duty Cycle • Duty Cycle Measurement Procedures. Frequency is the number of cycles produced per second measured in hertz (Hz).

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Chapter 10

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  1. Chapter 10 Measuring Frequency and Duty Cycle Frequency • Frequency Measurement • Frequency Measurement Procedures • Measuring Frequency with Clamp-On Meter • Duty Cycle • Duty Cycle Measurement Procedures

  2. Frequency is the number of cycles produced per second measured in hertz (Hz).

  3. Frequency measurement is displayed after connecting test leads to the circuit when using a DMM with a Hz setting.

  4. Frequency measurement using a DMM with a Hz button requires first measuring AC voltage.

  5. The frequency measurement of an electric motor drive output current can be used to calculate the speed of a motor.

  6. A load that is turned ON and OFF several times per second has a duty cycle.

  7. An automotive electronic fuel injection system uses pulse-width modulation for precise control of fuel supplied to the engine.

  8. When measuring duty cycle, the DMM displays the amount of time the input signal is above or below a fixed trigger level.

  9. On most DMMs, the Hz button is pressed twice for Duty Cycle mode.

  10. Review • What are the two standard power frequencies used throughout the world? • 60 Hz in the United States, Canada, and most of the Caribbean. • 50 Hz in Europe, Asia, much of South America, and the rest of the world.

  11. Review • What procedures are followed when measuring frequency with a DMM that includes a Hz setting? • Set the function switch to Hz. • Plug the black test lead into the common jack. • Plug the red test lead into the voltage jack. • Connect the DMM to the test circuit. • Read the frequency measurement displayed.

  12. Review • What happens to the speed of an AC motor if the frequency is decreased or increased? • If the frequency is decreased, the motor speed is decreased. • If the frequency is increased, the motor speed is increased.

  13. Review • What is the duty cycle and how is it expressed? • Duty cycle is an alternative frequency measurement that is the ratio of time a load or circuit is ON to the time a load or circuit is OFF. • Duty cycle is expressed as a percentage.

  14. Review • What procedures are followed when measuring Duty Cycle with a DMM? • Set the DMM to measure duty cycle. • Plug the black test lead into the common jack. • Plug the red test lead into the voltage jack. • (continued on next slide…)

  15. Review • What procedures are followed when measuring Duty Cycle with a DMM? • Connect the DMM to the test circuit (match polarity in DC circuits). • Read the duty cycle measurement displayed. A positive symbol (+) indicates ON time percent voltage measurement. A negative symbol (–) indicates OFF time percent voltage measurement.

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