A VFD creates an approximation of a sine wave by pulse width modulating a high frequency carrier. The carrier frequency is high enough that the motor effecively filters it out, leaving the sine wave. The frequency of the sine wave is varied to control the speed of the motor.
This is not really much use to Mach2 as it is only the commanded speed to the motor. It does not mean the motor will actually turn at that speed. The best thing to do is fit a sensor on the spindle and have done with it. That way Mach2 always knows the true speed of the spindle.
Les
Andy Wander wrote:
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I can't speak about the intricacies of the VFD, but PWM is Pulse Width
Modulation, where the ONLY thing that is varied is the width of the "ON"
pulse(not both ON and OFF). This means that the frequency of the pulses does
NOT change, just the ratio of ON-time to OFF time of a (quasi) square wave.
If the width of both the ON and the OFF pulse changed(and was identical, you
would NOT have PWM, you would have FM(frequency modulation) of a square
wave. Andy Wander
Verrex Corporation
