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Sensor to use and coil geometry?

Richard Lee50
Prodigy 50 points
Other Parts Discussed in Thread: LDC1101

Hello,

I would like a suggestion on the Sensor I should use and the coil geometry for the following application.

The target is 2mm wide with the geometry shown. We are trying to get 12bit resolution over the 180° rotation from 23mm to 21mm (2mm change in distance from the coil).  We would like to sample at a minimum of 1kHz (prefer 2kHz). I am considering the LDC1101. What shape and size of coil should I target?

Thanks, Rich Lee

  • 0
    TI__Genius 13650 points
    Hi Richard,
    we have an LDC1314-based rotational encoder reference design here, which contains full coil and target design: www.ti.com/.../TIDA-00508
    More information on coil designs is also available here: www.ti.com/.../snoa930.pdf
  • 0 in reply to Ben Kasemsadeh
    Prodigy 50 points

    Hi Ben,

    My design is only sensing the 2mm edge of the target, not the side of the target. So I am sensing the distance of the edge of the target over a 2mm range.  This diagram may be better.

    Regards, Rich

  • 0 in reply to Richard Lee50
    TI__Genius 13650 points
    Hi Rich,
    Is 'lateral position tolerance' in your diagram the left-right tolerance between coil and target in the center portion of your diagram? If yes, then I don't think this mechanical arrangement is feasible with your requirements and a single coil.

    If it is another tolerance, then I recommend using a circular coil. I recommend making it as large in diameter as possible, and bringing it as close to the target as possible. Note that with a single coil, you will not be able to achieve 360 degree coverage because the top and the bottom of your target have the same amount of coil coverage. You may need multiple coils to do 360 degree of coverage, and to do cancellation on tolerances.
  • 0 in reply to Ben Kasemsadeh
    Prodigy 50 points

    Hi Ben,

    The target has two lateral positions with respect to the coil in the center diagram.  The 2 positions are 0.6mm apart.  The target will be in Position 1 (-0.3mm off center of the coil) and rotate 180°. It will then transition to Position 2 (+0.3mm of center of the coil) by moving 0.6mm laterally.  It will then rotate back 180°.  This repeats by transitioning back to postion 1 and rotating 180°, etc.

    Regards, Rich Lee