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Noise in the quadrature channels QEPA and QEPB

Yuriy Sikalov
Intellectual 615 points


Hello,

Rotor speed sensor module is calculated by module QEP. There is noise in the quadrature channels QEPA and QEPB, which creates problems when calculating a rotor speed of the encoder. Can I filter out by program the noise channels?

Thank you!

  • 0
    Expert 1150 points

    Hello Yuriy,

     

    As far as i know there is no possibility for the program filtration of the QEP's input data stream because QEP hardware make all the job. In case you use quadrature-count mode you must have no problems with noise because of the noise immune properties of the quadrature encoder interface. 

    You can perform some addition filtration of the QEP module results in your software (for example a median filter) but you must keep in the head the  additional delays introduced by the filter which can reduce your control system stability.  Also you can improve noise immunity of the your hardware.  

    Typical industrial quadrature encoders  use RS-422 levels for it's outputs so I can't imagine the source of the noise which can cause problems for the speed calculation. 

     

    Best regards,

    Roman 

     

  • 0 in reply to Roman Ermakov
    Intellectual 615 points

    Ok. Thank you for your anwer!

  • 0 in reply to Yuriy Sikalov
    Intellectual 615 points

    Nevertheless, I would like to have a filter input QEP same as used in the GPIO module. We will solve the problem of a hardware solution.

  • 0 in reply to Roman Ermakov
    Prodigy 30 points
    Hello Roman

    if the noise comes from QEPI or QEPS, it could be a disaster.
    Do you have any good idea for making a Low pass filter or deconce to eQEP?
  • 0
    Genius 5885 points
    Yes you can. Use the GPIO input qualification. I have used it with success. But the speed measurement will have an additional error. You should measure speed by measuring more than one period of A (or B) signal (use cap prescaler). I prefer getting the speed through position measurement and alfa-beta filter, where speed estimate

    Regards, Mitja
  • 0 in reply to Mitja Nemec
    Prodigy 30 points
    Hello Mitja

    Thanks for your information!!!
    It helps a lot!!!
    You have perfect method for de- bouncing eQEP in C2000.

    But I made a mistake here....actually my CPU is AM437x(just like AM335x)
    the CPU's eQEP function is the same with C2000, but the GPIO MUX is totaly different.
    AM437x also has debounce function in GPIO MUX, but it's an other disaster....the basic frequency is 32KHZ
    Meanwhile, 33us, 66us,100us......lol

    Any way, thanks for your help!!!

    Regards,Snaken