Duty cycle is defined as:

• A. The total time the device is turned on during a treatment session
• B. The frequency of the pulses
• C. The percentage of time the machine is delivering output
• D. The sum of on and off times for a duty period

Answer: (C)

Duty cycle describes the proportion of time the device is delivering electrical output during each pulse cycle, usually expressed as a percentage. It is found by dividing the on-time by the total cycle time (on-time plus off-time) and multiplying by 100. This differs from the total time the device is on during a treatment session, which would simply add up all on-times across cycles and doesn’t reflect the pattern within each cycle. It also isn’t the pulse frequency, which measures how often cycles repeat per second, nor is it the cycle duration itself, which is the sum of on and off times. For example, if the device is on for 2 ms and off for 8 ms in each cycle, the duty cycle is 2 / (2+8) × 100 = 20%. A higher duty cycle increases the average current and potential heating, while a lower duty cycle limits them.