implement a dither signal on a pwm signal to control a servo valve

Discussion in 'General Electronics Chat' started by navidelec, Jan 7, 2015.

  1. navidelec

    Thread Starter New Member

    Jul 12, 2014
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    I would like to implement a dither signal (about 10 Hz or 300 Hz) on a pwm signal to control a servo valve, what is the requirements and limitation through this?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The main requirement is that the PWM frequency be higher than the Nyquist limit of twice the highest modulation frequency. For good response a value at least 10 times the highest dither frequency or ≥3000Hz is recommended..
     
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  3. navidelec

    Thread Starter New Member

    Jul 12, 2014
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    dear friend, I should take this requirement as a report to my presentation, where can I find this requirement for pwm and dither, I mean a text or book or ...?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Look up Nyquist sample rate. This applies to all sampling systems including PWM.
     
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  5. navidelec

    Thread Starter New Member

    Jul 12, 2014
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    But my servo valve current is so high (about 1 amp) to be applicable due to 3000Hz PWM, I wnoder if you tell me what should I do?
     
  6. crutschow

    Expert

    Mar 14, 2008
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    The servo likely has inductance which will smooth and average the PWM pulses into a steady current, which is what you want. A higher frequency actually helps, since there is less ripple in the average current value.
    The PWM driver just needs sufficient current capacity to provide the 1 amp current.

    Do you understand how PWM works?
     
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  7. navidelec

    Thread Starter New Member

    Jul 12, 2014
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    yes, i got it.
     
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