W223N735 Saratoga Drive
Waukesha, WI 53186
262-970-8660
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PULSE WIDTH MODULATION (PWM)
SOLENOID OPERATION
As with any solenoid, proportional solenoids are basically an inductor due to the coil winding. When a step voltage is applied to the winding, the current builds up to it's maximum current over a given period of time. If the step voltage is removed before reaching it's maximum value, the proportional solenoid will only move through a portion of its stroke and then begin returning to the zero position.
Shown in the Force Vs. Stroke graph is a typical hydraulic valve control, but throttle control solenoids can have much longer strokes with very flat force profiles based upon modifications of the units magnetic properties and overall design configuration.
If the voltage steps are applied at a repeated frequency (normally 20 to 100 Hertz) and the percentage "on time" (high voltage) is varied from 20 to 80 percent, the current applied to the solenoid will vary and the force created by the solenoid will vary from minimum to maximum. This type of voltage control, where the percent on time is varied, is called a "pulse width modulation" (PWM) control. For example, with a PWM signal at 100 hertz, each cycle will be .010 seconds long. A 40 percent modulation signal will have full voltage for .004 seconds and no voltage for .006 seconds each cycle.
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