How to Calculate a Duty Cycle
Duty cycle is defined as the time a device is in one of two states, divided by the time a device is in both states. A state could be defined as on and off such as with a light, or just a general condition such as slow or fast, or gaseous or liquid.
Duty cycle calculations are often required in electronic circuit design and automotive tuning applications. Timers, an electronic device often used to control how long an electronic device will be on, require that you understand how to calculate duty cycle to use them. Electronic and automotive technicians also must understand how to calculate duty cycle to troubleshoot electronic and electromechanical circuits.
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Instructions
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Construct a waveform, also referred to as a state diagram, on graph paper. Draw a horizontal straight line of any arbitrary length. For this example, draw a horizontal line that measures 10 units. At the endpoint of that line, draw a vertical line upward. Note its length. For this example, 5 units is used. From that endpoint, draw a horizontal line that measures 8 units. Finally, from the endpoint of that line, draw a vertical length downward with the same measure as the first vertical line, 5 units. Label the lower horizontal line, "Off State." Label the upper horizontal line, "On State." Note that the vertical lines could be any arbitrary length. These lengths are not used in the calculation.
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Sum the on and off time. For this example the sum of the on and off time would be 18, since 10 plus 8 is 18. Call this result the "total time."
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Calculate the duty cycle. Divide the "on time" by the "total time" and then multiply by 100. For this example, this would be 44 percent, since 8 divided by 18 is .44 and 100 multiplied by .44 is 44.
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Practice calculating different duty cycles. For example, draw a waveform exactly as was done in step one, but use two horizontal lines that each have a length of 10 units. The duty cycle calculation will be 50 percent. Devices that are "on" the same amount of time they are "off" always will have a duty cycle of 50 percent.
Consider a device that is always in just one state, the on state, will have a duty cycle of 100 percent. Perform the calculation that will verify this. Conversely, consider the fact that a device that is never on, always in the off state, will have a duty cycle of 0 percent. Perform the calculation to verify this. Remember that a duty cycle always has two states. However, one state may never occur. Remember the naming of the states is arbitrary.
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Tips & Warnings
Consider that duty cycle is most often used to describe a digital electronic waveform, a waveform that has two states, a logic one state and a logic zero state. For this application, think of duty cycle as the percentage of the time the waveform is in the "logic one" state divided by the amount of time that the waveform is in the "logic one and logic zero" states.
Consider that the duty cycle can also be used to describe the characteristic waveform of light. In this case the duty cycle is calculated in a similar fashion; that is, duty cycle would be calculated by dividing the time the light is on by the sum of the on and off time of the light. Turn on a flashlight and measure the time it is on. Then turn it off and measure the time it is off. Turn the flashlight back on again, to establish the end point of off time. Calculate the duty cycle from these time measurements.
References
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