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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 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).
Frequency measurement is displayed after connecting test leads to the circuit when using a DMM with a Hz setting.
Frequency measurement using a DMM with a Hz button requires first measuring AC voltage.
The frequency measurement of an electric motor drive output current can be used to calculate the speed of a motor.
A load that is turned ON and OFF several times per second has a duty cycle.
An automotive electronic fuel injection system uses pulse-width modulation for precise control of fuel supplied to the engine.
When measuring duty cycle, the DMM displays the amount of time the input signal is above or below a fixed trigger level.
On most DMMs, the Hz button is pressed twice for Duty Cycle mode.
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.
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.
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.
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.
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…)
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.