What is Duty-Cycle?
The duty cycle is the ratio of the duration that a load or circuit is ON to the duration during which the load or circuit is OFF.
The duty cycle, sometimes called ‘duty factor’, is expressed as a percentage of the ON time. A duty cycle of 60% indicates that a signal is ON 60% of the time and the remaining 40% OFF.
Many loads are quickly switched on and off via a fast-acting electronic switch that accurately manages the output power of the load. Load operation-such as the brightness of a lamp, the output of a heating element and the magnetic strength of a coil-can be controlled on a duty-cycle basis via periods of ON and OFF or cycles per second.
Duty-cycle simplified
If the atomiser is pulsed ON with varying duration (this is called pulse width modulation), the duty cycle is always different. If the atomiser is pulsed ON for 0.05 second in a 0.1 second cycle, the duty cycle of the fuel atomiser is 50%. If the atomiser is pulsed ON for 0.09 second of the same 0.1 second cycle, the duty cycle of the fuel injector is 90%.
Example of duty-cycle
In a car electronic fuel injection system, voltage pulses fed to the fuel injection valve solenoid control the fuel injection valve at a fixed rate of 10 cycles per second or 10 Hz.
Pulse width modulation allows precise electronic control of the fuel supply to the motor. The average voltage for each duty cycle is determined by the amount of pulse time ON.
Duty-cycle controlled solenoid valves use a variable duty-cycle signal to vary the flow or adjust the pressure. The longer a solenoid valve stays open, the greater the flow and the lower the pressure built up. These solenoid valves are controlled by the power supply or ground.
What is pulse width?
Pulse width is a measure of the actual duty cycle in milliseconds. The time OFF does not affect the pulse width of the signal. The only value measured is how long the signal is ON (controlled by the ground).
Reference: Digital Multimeter Principles by Glen A. Mazur, American Technical Publishers.
