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Gesture/Proximity Sensing with distance of 5cm

Ting Ye
Genius 11800 points

Hello Team,

If the sensed object is hand and distance is 5cm btw coil and the object, what inductance is needed for the coil?

The eddy current range of LDC1000 is about 800-ohm to 4M-ohm. Could you comment on eddy current formula and sensed object resitivity? How do I know if LDC is able to oscillate when the sensed object, conductive material varies?

I'd appreciate any comments.

Thank you!

Regards,

Ting

  • 0
    TI__Expert 4890 points

    Hi,

    1, The sensing distance is relate to the diameter of the coil rather than the inductance of the coil, please refer to FAQ.

    2, I think you may set a  large Rp range, then do some experiment to make sure the Rp is in the exact range when sensing different boject.

    Regards, Sunny. 

  • 0 in reply to Sunny Qin
    TI__Genius 11800 points

    Hi Sunny,

    Thank you for replying.

    So  there is no formula regarding eddy current loss and sensed material and only experiments with different inductance can proved if with distance of 5cm LDC will work?

    Thanks.

    Regards,

    Ting

  • 0 in reply to Ting Ye
    TI__Intellectual 1290 points

    Ting,

    Sensing a hand from 5cm is not easy with LDC1000. The eddy current is very small becuase the conductivity of human boy is very low (relative to metal). I don't think it is practical.

    Don

  • 0 in reply to Don Liu
    TI__Genius 11800 points

    Hello Don,

    Thank you for answering. I agree that the inductance of the sensor will need to be quite large and with low Rs at sensing distance of 5cm and sensed object of hand. Just curious if there is formular that can show sensed material conductivity, distance, and induced eddy current so that we can know if Rp is out off LDC sensed range. But thank you for confirmming the feasibility of this case.

     

    Thanks.

    Regards,

    Ting

  • 0 in reply to Ting Ye
    TI__Intellectual 1290 points

    Ting,

    I am afraid ther is no such formula. That is why simulation is the normal method to estimate the performance. Such simulation usually takes hours to complete.

    For very challenging application like this one, the high frequency resistance Rs must be made very small, and coil diameter large enough. Multi-strand wire can reduce Rs and can be used to wind the coil.

    Best regards,

    Don