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TMS320F28069M: eQEP

sachin shenoy k
Prodigy 10 points

Part Number: TMS320F28069M
Other Parts Discussed in Thread: DESIGNDRIVE

While going through the eQEP, i came across the velocity calculation rate. Can anyone tell me is there any thumb rule to set the velocity calculation rate. I saw an example where the SYSCLOCKOUT=100Mhz and velocity calculation rate is 400 HZ. is there any particular reason for chosing 400 Hz

  • 0
    Guru 30330 points
    Sachin,

    This is purely up to the application. You will need to find a balance around your low speed velocity calculation. At low speeds, the velocity calculation has the potential to read zero if your calculation rate is too short. i.e. the shaft has changed positions, but not enough to increment the QPOSCNT between readings. Your velocity will read 0 even though there is SOME velocity. At higher speeds you could protentially sample too slowly and have the QPOSCNT overflow, thus causing and error in your velocity calculation.

    The Introduction section in the TRM provides a sufficient example including transitioning between the two equations based on a velocity threshold, and an encoder that provides the appropriate pulse train.

    At very low speeds, another options would be to transition your application to use an absolute position sensor such as a SinCos transducer. Refer to this video on our DesignDRIVE Position Manager training.ti.com/designdrive-position-manager-sincos-and-resolver-solution-introductions for more information . This really is only applicable if you have an absolute encoder available in addition to the incremental encoder providing the quadrature pulse train.

    Regards,
    Mark