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Re: [mach1mach2cnc] Re: Question on index pulse

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  • Les Newell
    Hi Andy, If you average a steady state PWM signal (apply a low pass filter) you get a DC voltage. At 0% PWM you get 0V, at 50% PWM you get 1/2 voltage and at
    Message 1 of 15 , Mar 1, 2004
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      Hi Andy,
      If you average a steady state PWM signal (apply a low pass filter) you
      get a DC voltage. At 0% PWM you get 0V, at 50% PWM you get 1/2 voltage
      and at 100% PWM you get full voltage and so on.
      Now if you slowly change the pulse width your DC voltage will slowly
      change to follow it.

      A VFD changes the pulse width in a sinusoidal pattern and the motor
      inductance acts as the filter. As long as the PWM frequency is much
      higher than the sine wave frequency (say 10kHz or highter) all the motor
      will see is the sine wave. By varying the pattern the VFD can control
      the sine wave frequency and voltage.

      Les


      Andy Wander wrote:

      > Les:
      >
      > Thanks for the explanation-what I still don't understand about it is how the
      > "Sine Wave", which is generated by the "filtering" of the motor, will vary
      > in frequency, if the only thing that is done to it is to change the PWM duty
      > cycle. This would seem to me to get us to a "Sine wave" which has different
      > values for it's Positive and Negative half-cycles, but I can't see how the
      > frequency would change unless the frequency of the PWM changed.
      >
      >
      > Andy Wander
      > Verrex Corporation
      >
    • Art
      ... pick up the true speed of a machine. Can the PWM frequency of a VFD be used for this? If so, can it be scaled in MACH2 to correspnd No. This can only be
      Message 2 of 15 , Mar 1, 2004
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        Jeff:

        >> notice that "index pulse" can be checked on the parallel input to
        pick up the true speed of a machine. Can the PWM frequency of a VFD
        be used for this? If so, can it be scaled in MACH2 to correspnd

        No. This can only be gotten for a once per rotation pulse from the spindle
        sensor..

        Art
        www.artofcnc.ca
      • Ed Gilbert
        Hi Andy, Are you actually talking about the signals on the wires to the motor or about a PWM signal generated by the VFD to indicate the frequency it is
        Message 3 of 15 , Mar 1, 2004
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          Hi Andy,

          Are you actually talking about the signals on the wires to the motor or
          about a PWM signal generated by the VFD to indicate the frequency it is
          running at?

          Mach2 uses the index pulse to determine RPM and is probably based a number
          of pulses per interrupt cycle. It may be based on the speeds you define in
          the pulley setup of the spindle. You would have to ask ART specifically.



          Best,

          Ed Gilbert

          Gilbert Engineered Systems
          632 Warrenton-Embro Road
          Macon, NC 27551
          252-257-0539
          > -----Original Message-----
          > From: Andy Wander [mailto:awander@...]
          > Sent: Monday, March 01, 2004 12:05 PM
          > To: 'mach1mach2cnc@yahoogroups.com'
          > Subject: RE: [mach1mach2cnc] Question on index pulse
          >
          > Of course, VFD means Variable Frequency, so is this actually a PWM signal?
          > I'm so confused...
          >
          > Andy Wander
          > Verrex Corporation
          >
          > -----Original Message-----
          > From: washcomp [mailto:jeff@...]
          > Sent: Monday, March 01, 2004 8:42 AM
          > To: mach1mach2cnc@yahoogroups.com
          > Subject: [mach1mach2cnc] Question on index pulse
          >
          > I notice that "index pulse" can be checked on the parallel input to
          > pick up the true speed of a machine. Can the PWM frequency of a VFD
          > be used for this? If so, can it be scaled in MACH2 to correspnd to
          > the speed (I believe speed is a linear function to frequency, but the
          > numeric value of one will not be the same as the other.
          >
          > Jeff
          >
          >
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